Scientific Knowledge

According to Aristotle, there are three types of knowledge:

1) Perception of particulars; knowledge given by the senses

2) Experience; memories arrived at by induction based upon experience, e.g. this is a chair and so I can sit on it

3) Scientific; knowledge both of what is the case, and why it is the case

When deducing from experiental knowledge, the premises can be true but the conclusions false. For example, I might conclude from my experience of chairs that all chairs I sit on will take my weight. But this is not necessarily true, and cannot be thought of as scientific knowledge since we have no reason to believe the conclusion, no reason why it should be the case.

An example of deduction that would yield scientific knowledge:
1) Lights that are relatively near the earth do not twinkle
2) All visible planets are relatively near the earth
All visible planets do not twinkle

An example of deduction that wouldn't yield scientific knowledge:
1) All visible planets do not twinkle
2) Every light that does not twinkle is a relatively near light
Every visible planet is a relatively near light

Example two is unscientific because we have no reason to accept the first assumption without reference to the second assumption and the conclusion. With example one, although the two assumptions aren't self-explanatory, they don't assume each other nor the conclusion, and so the conclusion is scientific.

All scientific knowledge can therefore be reduced to certain first principles that are self-explanatory. For example:
Q) why are cows deficient in teeth?
A) because they have four stomachs to digest the food
Q) why do they have four stomachs?
A) because they are ruminants

The final answer is self-explanatory. To be a ruminant is part of the essence of a 'cow', and so no further explanation is needed.

Objection: Do we not have scientific knowledge of contingent and particular matters of fact? Does the theory of coherence, in contrast to the foundationalist picture offered by Aristotle's theory of scientific knowledge, suggest that we can have scientific knowledge without necessarily needing to derive that knowledge from first principles? For example, can we treat the theory of evolution as scientific knowledge? According to Aristotle, it is merely experiential knowledge, conjecture. But then science must either concern itself equally with conjecture and that which Aristotle considers scientific knowledge, or admit that it knows very little indeed.

Objection: furthermore, Aristotle's conception of scientific knowledge negates the use of interpolation and extrapolation, of quantitative prediction, since the only reason we have to believe some knowledge based upon those methods is experience. Whilst it is true that science generally seeks more reliable explanations than those that are by nature experiential, it again seems to be an essential part of science that Aristotle would neglect.

Objection: Can we really find self-explanatory first principles for all of science? It seems that often we find even our first principles require other first principles to be explained, and that we tend to generalise explanations until a first principle that coheres can be found. Gravity is a good example here, since it itself is not self-explanatory, but we treat it as a first principle in order that we might understand almost all physics, except that which attempts to explain gravity of course.

In general, regardless of the problems specific to Aristotle's division between experiential and scientific knowledge, one can draw out a general method of learning from his distinctions:

Perception --induction--> Experience --dialectic--> scientific knowledge

And finally, Aristotle tackles the question of metaphysics, and how that is different from physics and the other sciences. He concludes that there is a special kind of scientific knowledge, wisdom, that concerns itself with the most universal causes, and that wisdom is that which metaphysics supposedly yields.

Dialectic

If scientific knowledge is based upon first principles, how can we come to know first principles? If we claim that 'all cows are ruminants' is a first principle, in that it described the essence of a cow, then we need to be able to develop it into a full explication of the essence of a cow (e.g. 'cows are herbivorous, hoofed animals...'). Dialectic allows us to do this.

The process of dialectic is:

1) Begin from existing and conflicting opinions of reputable sources
2) Deduce the implications and problems that the endoxa face, and the implications of these problems
3) Evaluate the conflicts and problems according to agreed beliefs to which there is no worthwhile opposition (endoxa)
4) Reconcile the differences and conflicts until you arrive at an unobjectionable compromise

Why trust dialectic?

Since the opinions taken from (1) have been formed from some reasoning, it is plausible that each of them will have some truth in them, and that therefore the conclusion (4) will contain some truth.

Through taking step (2), we gain a clearer understanding both of the problems we must resolve, without which we cannot begin the process (akin, Aristotle says, to trying to untie yourself without first studying the knot). And through taking step (3) we can evaluate each opinion with this clearer understanding and so be in the best possible position to recognise and deduce the elements of truth, and weed out false aspects of the beliefs.

Objection: Dialectic undoubtedly gives us a coherent set of beliefs, but why should we assume that these accurately represent the objective truth? Particularly when we use dialectic to establish first principles, are we not just allowing our methodology to deceive us, when in fact we may deduce entirely false first principles and so build all of our knowledge on false foundations?

Reply: Though one may be able to make quite a large web of coherent beliefs that are entirely false, at some point you will inevitable find anomalies, and so will be forced to evaluate the entire web against those anomalies.

Objection reply: But if we are evaluating these anomalies in the context of their coherence with the web, and in particular with endoxa, they will simply discounted. To allow for radical new ideas to upset the web, and so to assure us that dialectic is able to get us closer to an objective truth, we must ignore the endoxa or be open to the idea that the endoxa may be entirely wrong, e.g. evolution upsetting ideas of creationism, anthrocentrism, etc.

Aristotle's responses:
a) We have no choice but to rely on the beliefs we have, and the beliefs that these lead us to
b) Those reputable beliefs we start out with are intrinsically justified, and so do not require justification from other beliefs, though some may be undermined by enquiry in the future
c) Some beliefs are necessary conditions for rational discourse

Objection 2: Through dialectic, Aristotle wants to establish first principles. In Metaphysics, Aristotle says dialectic will also establish universal truths. But necessary truths are objective, and coherent truths can only be contingent, since we have Little reason, except that it hasn't yet happened, to suppose those belief will always be true.

Possible replies: That we have no better way of knowing of objective truth; that, as in (c) we have no choice in accepting certain beliefs in discourse

Can, then, metaphysics have any claim on truth? Or is it simply experiential deduction?

And my essay on this subject:

Does Dialectic enable knowledge of reality? Why or why not?

In his enquiries in metaphysics, the natural and social sciences and mathematics, Aristotle employed a method of acquiring knowledge called dialectic; he thought that dialectic was the only method available that could be said to establish knowledge as opposed to belief. This view predominated for over one and a half millennia, and has in the past few hundred years been further developed and extended in various different ways to provide many quite different understandings of what constitutes knowledge, and by what methods we can acquire knowledge, and even if we acquire knowledge at all. Given the epistemic ambiguity of dialectic itself, it is perhaps best to begin by studying its roots in Aristotle's writings, and to analyse its key problems there.

In Topics, Aristotle set himself the task of explaining and justifying dialectic as the only method of acquiring knowledge because he wanted to "find a line of enquiry whereby we shall be able to reason from opinions that are generally accepted" (Topics, 100a 19-20). In other words, he wanted to avoid situations where critics could doubt his premises and so undermine his arguments, and so sought to establish, in most of his works, first principles upon which his other fields of enquiry, from philosophy to botany, could be soundly and unobjectionably based. Once established, these principles could be employed in further dialectic, expanding our field of knowledge in a reasonable manner.

So what is dialectic? As a form of learning, it involves four stages: One begins with two or more conflicting opinions that come from reputable sources (that is to say from those whom we deem to be learned already); then, one deduces the problems posed by each opinion and the implications of these problems, and the problems and implications of the conflict between the two opinions; thirdly, one evaluates each opinion according to a set of agreed beliefs; and finally one can reconcile the differences between the two opinions, finding, according to Aristotle, the truth within the resultant unifying opinion.

Why take this approach? To begin with, Aristotle suggests, we are more justified in our certainty if we have good reason to believe the opinions we begin with, as opposed to taking two radical and unpopular views, since they will be based upon good rational or commonsense arguments. Though this may be the case, it does present a significant problem, since it doesn't allow for radical changes in our belief system; we might instinctively ask whether or not we would have taken Darwin or Einstein at all seriously if we were to only allow dialectic as a route to knowledge. This however slightly misses the point, since both Darwin and Einstein did base their work upon the ideas of others, and so developed their radical theories in the context of an acknowledged new belief system that itself was worked upon by reputable sources. In fact, it is common sense that we don't take a proposition seriously unless we have reason to believe that the proposer is at all likely to be correct. Quite how far we take this is unclear in Aristotle's writing, and could range from only accepting the work of already-eminent theorists (which begs the question as to how anyone could ever ascend to that position unless they were apprentices to eminent theorists) to accepting any opinions from anyone with a reasonable formal education.

Once we have the two conflicting reputable opinions, Aristotle says that there must be some truth in each opinion, else the sources would not hold them to be true, and so we must begin to find what truths can be found in each. This is best done by first isolating the key problems with each; Aristotle compared this to untying a knot, and pointed out that one could not begin to untangle the knot until one first appreciated that the knot exists, and further by appreciating the nature of the knot. By analysing the endoxa we not only find that seems unlikely about them, but also points in common between the differing views. From here, it is a matter of employing rational arguments to find the truth within the statements, almost as if in a dialogue between two people.

So it seems that we have some reason to trust that dialectic might provide us with relatively unobjectionable conclusions, but why employ this method at all, since no other academic disciplines use it? 'Philosophy', according to J. D. Evans, can be 'distinguished by its methods and focus of interest' (Evans, p.2). If its primary method is dialectic, then it is because philosophy is not just 'occupied with purely conceptual problems rather than substantive issues of fact' (Evans, p.3). Philosophers must appreciate ideas from a diverse range of disciplines that may not have a single method acceptable to each discipline that could unite them. For example, one might want to use substantive facts of biology to influence an argument over the nature of the mind; since these two discussions are methodologically incompatible, one needs a method that can unite them and cross over axiomatic bases. That method is dialectic.

But if this is true, then we must accept the assumption that all knowledge needn't reduce to the same axiomatic bases, which seems like a fairly troubling conclusion, especially given Aristotle's commitment to first principles. If we are to accept the idea of first principles, we must consider the possibility that there is at least a substantial number of principles that form more than a collection of priori and logical truths upon which all disciplines are based. We must do this if we accept the epistemological position known as foundationalism, according to which every belief is based upon some others, and those others are based on yet more fundamental beliefs, and that this pattern continues until one finds foundational beliefs that are based upon no other, i.e. they are self-evident or a priori truths. If we accept foundationalism, then we must accept that every truth can reduce to the foundational truths, and can be explained purely in terms of these foundational truths, in the same way that all of mathematics can be proved in terms of a few logical and observed truths. So in this case, why should we think of dialectic as a useful way of discovering foundational beliefs, let alone other less fundamental beliefs, if it doesn't work from a single axiomatic base, but rather covers all it encounters? Should we not, as Descartes proposed, begin from the foundations and work our way up the 'knowledge tree'?

Aristotle provides a clear answer to this, but one that confuses his epistemological position and brings into doubt his claims for first principles. He emphasises, through his justifications for dialectic, that what is important is that the beliefs we acquire cohere, hence dialectic is such a good method, since it finds incoherence in conflicting beliefs and resolves it, until, conceivably, we have one coherent set of knowledge that is the truth about everything. According to this view, there simple aren't any foundational beliefs, they're an illusion or misconception; those truths that are self-evident or a priori are simply not 'knowledge' at all, at least not in the sense that 'John is wearing a green hat' is knowledge. To say: 'a bachelor is an unmarried man' is not to express any knowledge about those two terms, but rather to express an appreciation of their nature, their definition. To say: '1+1=2', meanwhile, is simply to show that one appreciates the way in which language conceptualises logical truths about reality. To then say: 'John has one green hat and has bought a new green hat, and so has two green hats' is to express knowledge, based upon its coherence with one's observations of John's hat collection according to logical truths. Other supposedly 'foundational' beliefs may simply have very small 'webs' of coherence upon which they are based, and so appear foundational when compared to more complex beliefs, e.g. how trees grow.

So, if we take a coherentist epistemological stand, the role of dialectic is to work on beliefs until we eventually find entirely self-contained webs of truths. Of course, Aristotle still holds that we can use strong dialectic to find first principles, but in a sense strong dialectic only helps us to discover the logical, a priori and linguistic truths upon which all of our arguments are based.

There remains, however, a serious worry about this stand, for 'coherence within common beliefs does not seem to be a ground for claiming to have found objective principles' (Irwin, p.8). Aristotle can't ever be immune from scepticism, from the doubt that his whole web of knowledge is in fact wrong and that, if he were to reassess his first principles or find a major new coherent web that conflicted with his current web, he might find that all that he had once believed was untrue. This criticism is especially telling of Aristotle's dialectic, because he placed such a lot of value on intuition, upon which many endoxa are founded. Aristotle himself believed the world to be spherical, but had he not, one wonders what he might have said to Copernicus when he challenged one of the most fundamental endoxa of his time. Again this susceptibility to doubt is made worse by the possibility of radical and unpopular opinions being closer to the objective truth than received and accepted opinions. Aristotle might have given this more thought had he considered his example of the knot more closely, for what use is it knowing that there is a knot if one refuses to take seriously the suggestion that one has completely missed the most important threads in the tangle? To work with a coherntist epistemology, one must surely scrap Aristotle's first step in dialectic and allow for all views, endoxa or not, to be considered. This really oughtn't be a big problem for Aristotle, since if a radical view is really completely false and baseless, then it won't take long under rational analysis and in comparison to endoxa to determine that it is in fact totally false. If, on the other hand, it is true, or closer to the truth than any endoxa, then it ought to animate in a dialectical investigation sufficient problems and questions to make it worth serious consideration, and so the truth ought to come out.

In this way also we can forget the worry of epistemological reduction, because even if they do all reduce to certain axiomatic or logical bases, we needn't know those bases nor the relationship of all knowledge to those bases in order to make a claim to knowledge, although being able to do such a thing would certainly strengthen a case for coherence.

Furthermore, because dialectic concentrates more on conserving endoxa where appropriate and developing them to resolve incoherence, and is interdisciplinary, we are more likely to acquire knowledge of reality, since any incoherence with reality will immediately be considered as a problem. Other methods of knowledge acquisition, on the other hand, may take the inquirer down one route ignoring other evidence, and so may ignore apparent facts of reality altogether in order to develop a particular theory or paradigm. In this sense, though we cannot say that dialectic gives us absolutely objective knowledge of reality, it does seem to give us more knowledge of reality, and a better knowledge of reality, than other possible methods and other epistemological systems.

Bibliography

Aristotle, Metaphysics, in The Basic Works of Aristotle, ed. R. McKeon, 2001

Aristotle, Topics, in The Basic Works of Aristotle, ed. R. McKeon, 2001

J.D. Evans, Aristotle (Philosophers in Context), The Harvester Press, 1987

T.H. Irwin, Aristotle's First Principles, Clarendon Press, 1998

Metaphysics and Being Qua Being

In tackling metaphysics, Aristotle starts with Plato's views, and more specifically of Plato's science of Forms and the Good. Thus Aristotle holds metaphysics to be the science of the first and most universal causes, rather than the attributes of things that have a contingent existence. Metaphysics is the study of "being qua being", or the study of attributes that belong to things merely insofar as they exist, e.g. existence, unity, sameness and difference.

The fundamental question posed by metaphysics is: what is true of existents insofar as they exist?

But by inheriting this definition of metaphysics, Aristotle is confronted with a problem, since he rejected Plato's theory of Forms and the good, and instead suggested that there are many senses of 'good', depending on what it is that you are evaluating. So too, he said, are there many senses in which things can be said to exist. Thus, it seems, there can be no science of existence and of universal causes, and so there can be no metaphysics.

Aristotle's solution is to demonstrate that there is a single, 'fundamental' sense of 'exist' from which the other senses derive, and that that sense of 'exist' is the subject of metaphysics. To do this, he first sets up some distinctions to distinguish between the various senses of 'exist':

Homonymous things are those which are both described by the same predicate but with different definitions, e.g. "I am Polish" and "I polish the floor"
Synonymous things are those which are both described by the same predicate and each with the same definition of that predicate, e.g. "I polish the floor" and "I buff the floor"

In some cases, one thing can be Homonymous with another because it is dependent upon it, in what is called non-coincidental homonymy. Where this is the case, there will be one word that has focal meaning amongst the homonyms, in that it is the one from which all other meanings are derived.

Thus, for Aristotle, the central question of metaphysics becomes: what is true of substance insofar as it exists?

Aristotle held 'existence' to be a collection of homonyms, with a focal meaning that applies to substances (e.g. the meaning it has in 'Socrates exists'). The two most distinct meanings of 'exist' that Aristotle drew out in relation to substances were:

1) Primary: a substance that exists in its own right, independent of others
2) Secondary: a substance that exists by virtue of its relation to a substance, dependent upon primary substances, e.g. colour (that flower is red), jogging (I am jogging)

Thus Aristotle draws two distinct areas of study for metaphysics.

Aristotle also tackled the question of mathematics; Plato held "1+1=2" to be a statement of substance, but Aristotle disagreed, thinking that numbers can only exist in relation to other primary substances, and so only a statement like "1 dog + 1 dog = 2 dogs" could be a statement about substance (in this case in particular it is a statement about dogs qua unity)

This marked a fundamental departure from Plato, since Aristotle suggested that we cannot understand truth without reference to physical things, in contrast to Plato's emphasis on the immaterial Forms.

The Principle of Non-Contradiction

The PNC: A property cannot both belong and not belong to a subject at the same time and in the same respect

The PNC is the most certain principle, i.e.:

1) It is not possible to be wrong about it
2) If you know anything, you know it (all statements of knowledge imply it)

But there are those who deny it, including para-consistent logicians. One possible objection is that this law only appears to apply to our use of language, and the way in which we frame our reality. One might also go so far as to say that the principle is, or could be, both true and false. Quantum mechanics might suggest that often we can't know either way, and so must deem the principle to be void and meaningless in many situations.

In response to the kinds of criticisms he could have anticipated or received, Aristotle said that those who deny the principle merely think they deny it, and that since they have knowledge they in fact do believe it. And in response to all those criticisms that still want to retain an understanding of truth and falseness, one can say that by simply asking the question, is the PNC true, you are assuming that it must either be true or false, and so affirming its truth.

But if the principle is so self-evident, and the criticisms so weak, why bother to mention it? Aristotle thinks that not only will it give us a clearer understanding of the role the principle plays in logic and therefore in philosophy, but also once irrefutably established it informs other discussions, in particular:

If the PNC is true, then not everything can be changing in every way, and so radical change must be false (more on this in the next article on change).

If the PNC is true, then relativism as a theory of reality must be false. If Jack believes the sun is shining, and Jill believes it is not shining, then one of the two must be false. This in particular is where the PNC contradicts physics, and so questions either the PNC, the theories of quantum physics, or the nature of the quantum level in relation to the super-quantum level.

Change

Aristotle asks: how is change possible?

For context, the pre-Socratic philosopher Parmenides thought that nothing can come from nothing, that what is cannot come or cease to be, and that change is therefore impossible. Change is merely an illusion, he thought, and the sum of reality, or even every aspect of reality, is an unchanging whole. Others contended that at all times everything changes in every way.

Aristotle agrees with Parmenides in his two assumptions, but instead concludes that there must be something permanent in all change; all change, in other words, is in a subject. For example:

1) The unmusical becomes the musical (Plato) must be false, since something is coming from a lack of that something
2) Socrates becomes musical is possible, since it is a change in the subject; Socrates acquires this musical ability from somewhere else.
3) The bronze is moulded into a statue is possible, since it is also a change in the subject; the subject, bronze, remains, whilst its form changes from unmoulded to moulded statue

Where does this change in the subject come from? According to Aristotle, from his potential for musicality and from his interaction with other objects and subjects; but Socrates takes nothing from the world when observing and learning from rhythm, harmony etc. and so the change is all in the subject, in the conversion from potentiality to actuality.

But given that Aristotle rejected the notion that everything changes in every way, what underlies change when a subject comes into existence? If we are composed of matter and form (and are therefore substantial complexes, e.g. a house is composed of bricks, and the particular arrangements of those bricks), then what changes: matter, form, or both? Aristotle thought that it was the form that changed, whilst the matter unerlies the change. The matter that Socreates' body was composed of didn't change, but its form did. The same applies to the bronze.

The form/matter distinction

This is a logical distinction useful in understanding the nature of substance. It holds that things (subjects & objects) are not identical to the matter that they are made up of:

1) My body's cells will die and be replaced as time passes
2) I will not be a different person because of the changing cells
I am not identical to my matter (according to Leibniz's law)
I am my matter + my form = my substance

Change is the actuality of the potential qua such, i.e. the actualisation of a potential within a substance whilst aspects of that substance's matter (and form) persist

This means:
1) Change is directional / teleological
2) Change is understood in terms of its culmination
3) Every change has a cause

Objection: quantum physics again makes some of Aristotle's ideas questionable. Changes at the quantum level and in the zero point energy field suggest that matter can come in and out of existence from nothing, and without direction. The quantum level seems so random that it disobeys all of his laws of change. This either means that we can allow for two sets of rules, or that one set is wrong; either change at the quantum level does obey Aristotle's laws, and we have yet to see evidence, or at the super-quantum level all change is random.

The Four causes

Causes are cited as answers to questions of the form: "Why is S P?", e.g. "Why is Socrates musical?". The Greek word Aristotle used was aition, for which there is no suitable translation in English; a cause, to Aristotle, was more than just a reason behind an event, it was the reason behind almost any "why" question. A complete answer, to accord with Aristotle's thoughts on knowledge, must take the form:

1) S is M
2) M is P
S is P

There are four distinct kinds of cause:

1. Material cause: "that out of which a thing comes to be, and which persists"
a) The statue is made of bronze
b) Bronze things are malleable
The statue is malleable.

2. Formal cause: "the essence," "the account of what-it-is- to-be, and the parts of the account."
a) The moon is deprived of light when screened by the earth
b) Things deprived of light by screening are eclipsed
The moon is eclipsed.

3. Efficient cause: "the primary source of change"
a) The child has a snub nosed father
b) Children of snub nosed fathers are snub nosed
The child is snub nosed.

4. Final cause: "the end (telos), that for the sake of which a thing is done"
a) Houses are shelters for belongings
b) Shelters for belongings are roofed
Houses are roofed.

Material and formal causes are preconditions for change, in that they allow for the distinction between matter and form in terms of change. They are static, in that they tell us what the world is like at the moment.

Efficient and final causes explain why things actually come to be what they are. They are dynamic, in that they explain why matter has come to be formed in the way that it has, and in doing so explain change.

Final causes require further elaboration:

1) The final cause of something is its proper functioning, its essence
2) Final causes are not something anyone need be conscious of

The essence of something could also be stated as a formal cause (a particular configuration of DNA) or even as an efficient cause (explanation of their DNA and environment as formative in their character). The final cause might today be considered to be 'ensuring its DNA persists', but Aristotle would definitely have said 'to perform its proper function in its community'.

Objection: suggesting natural things, as opposed to man-made things, can have final causes surely places an anthrocentrist or similarly deterministic view on the world. Even if we were to say the final cause of a tree is to absorb CO₂ and give out oxygen, we would be implying the sustainability of the earth's ecology determines the worth of every object on that earth. Whilst this might be acceptable to ecologists, it surely raises a serious problem for those who wouldn't subscribe to this deterministic view, nor any other.

This determinism seems to be particularly problematic in nature, but Aristotle attempts to address this. He says that the final cause of an object in nature isn't its purpose or intention, but rather the end of a regular development, e.g. the final cause of a developing tiger is to be a tiger. Natural objects that cannot have final causes in the way that Aristotle claims humans can therefore have final causes that can be identified with formal causes, though that is not to say that at any point in time a natural object's final and formal causes must be the same, since the formal doesn't take into account development and only describes the form at the time, whilst the final would describe the formal at the point of completion of the object's development.

Objection: suggesting everything has a final cause implies that substances have causes posterior to their effects. This isn't necessarily a problem for Aristotle, but it does make final causes seem even more deterministic. One could allow for final causes changing, e.g. a house becomes a tourist attraction, and so its final cause would change from being to be roofed to being to be a good tourist attraction.

Objection: the familiar theme of quantum physics again rears its head, but so too does randomness and chaos theory. Aristotle's theory of change doesn't allow for any randomness nor chance, which certainly coheres with the basis of the scientific methodology, but which runs aground in contemporary physics.

Primary substance

What could primary substance be?

Composite substances (e.g. a human being, a chair)
Matter (e.g. the stuff from which the chair is made)
Form (e.g. the essence of a chair)

What are the criteria for being a primary substance?

1) Separable (i.e. capable of existing independently of anything else)
2) Primary in knowledge (i.e. x is primary in knowledge iff knowledge of it is not dependent on knowledge of anything else.
3) An individual (i.e. a 'this something', thereby excluding the imaginary since the imaginary cannot have attributes that are matters of fact)

Composite substances cannot be primary substances because their existence is quite obviously not seperable from that of their form and matter. Though one can can be consider it in terms of its component parts, one cannot separate it from them and be left with a 'this something'. Because of this, it is also not primary in knowledge; matter and/or form are.

Matter cannot be a primary substance either. Though it seems to pass both the separability test (one can break a tree down into logs of wood) and the individuality test (one can say 'this tree' and 'this log'), it cannot pass both at the same time, i.e. one cannot take 'this tree', separate the matter from its form (e.g. chop it into logs) and maintain that same individual, since it is no longer 'this tree' but now 'these logs', and you are now dealing with a new substance (has new form).

Indeed, by separating matter from its form, it ceases to be individual, since one can no longer refer to it as a 'this anything'; whenever one refers to matter, one implicitly refers to its form as well. It therefore isn't primary in knowledge either, as to know of matter one must also know of that matter's form.

Therefore form must be primary substance, and Aristotle begins to substitute form for essence, perhaps to disassociate himself from Plato, since his theory of forms doesn't hold them to be universal constants instantiated in physical things, but as the arrangement, or essence, of matter, that disappears with that matter. It might also be because when we talk of something's form, we can mean many different things, e.g. "Aristotle is a botanist", "Aristotle is a philosopher", however when we talk of essence we focus on that which is universal and central to an object, e.g. "Aristotle is a human being that is most fulfilled in a polis"

But then is primary substance the essence of an individual object, or of a class or species of objects, e.g. "humans", "cliffs", etc.? In terms of solving the problem of 'what is primary substance' this really doesn't matter, but it should matter to Aristotle. According to his criteria, it could be either, depending on how you define and deploy the term "essence". To make as safe a definition of essence as possible (by safe I mean one that makes essence most unobjectionably primary) one ought to lean towards a species interpretation, but then we can also assert a very individualistic sense of each person on earth having their own unique essence, and so lean towards an individual interpretation.

Objection: even though essence can persist whilst the underlying matter changes, the essence couldn't survive the total removal of that matter except in language, where we can talk of A without mentioning A's matter. But even in language we implicitly posit the existence of A's matter when discussing A's form, and we cannot conceive of form without matter. One could also say that essence is separable in time, in the 4th dimension, since it is in that dimension that essence doesn't depend upon any particular matter. But again, it still depends upon some matter to exist, unless we can think of essence as existing solely in the 4th dimension and not having the three spatial dimensions.

Aristotle seems to share this assumption that form cannot persist entirely without matter, as he rejects Plato's theory of universal forms and physical instantiations, suggesting he was caught in between a theory of materialism and a theory of forms. If one were to interpret Aristotle's criteria for primary substance strictly, essense doesn't seem to comply; in other words, it looks as though Aristotle has simply been liberal with his interpretation to fit his form/matter distinction with his theory of primary substances.

Objection: if I melt down a bronze statue, the matter doesn't change, and underlies the change between two forms. I can also, in a sense, refer to the bronze as a 'this something' in saying 'this bronze' on both occasions. That appears to be two honomonous uses of the term 'this bronze', suggesting that matter is both separable, individual and primary in knowledge, something we can accept if we interpret Aristotle's criteria liberally. So Aristotle's loose interpretation runs into trouble here again.

Objection: can anything be considred primary? If neither complex substances nor their form nor matter can be definitively described as primary according to a strict interpretation of Aristotle's criteria, we must conclude either that his criteria are flawed or that there is no such thing as primary substance. Given the fairly arbitrary nature of any other criteria for primary substance, it would seem that the very idea is simply false, a philosophical illusion that Aristotle conjured up to fit into his theory of coherent knowledge with foundations.