Fourth Way

The Fourth Way of Thomas Aquinas


  1. Platonic Forms – Perfection in Being as the basis of knowledge and goodness

Heraclitus had understood that all material things are in a state of flux, i.e., everything in our experience is constantly changing.  He is famous for the saying “One cannot step in the same river twice.”

As W. K. C. Guthrie notes in The Greek Philosophers:

The Heracliteans maintained that everything in the world of space and time was continually flowing, as they put it.  Change never ceased to operate for a moment and nothing was ever the same for two instants together.  The consequence of this doctrine appeared to be that there could be no knowledge of this world, since one cannot be said to have knowledge of something which is different at this moment from what it was a moment ago.  Knowledge demands a stable object to be known.  Parmenides on the other hand had said that there is such a stable reality, which can be discovered only through the activity of the mind working altogether apart from the senses.  The object of knowledge must be immutable and eternal, exempt from time and change, whereas the senses only bring us into contact with the mutable and perishable.

(p. 88)

For Plato, following Heraclitus, knowledge, as a stable grasp of things, cannot arise from the things that one senses since these things are forever changing, and are not themselves ever stable.

Thus, while Plato accepts that material things are in a constant state of becoming, he also takes it as obvious that we do have knowledge, a grasp of stable, unchanging realities.  This is most evident in mathematics.  We do in fact know that 2 + 2 = 4, and that it has always been true, and will always continue to be true.  There is, in fact, some stable knowledge, but the problem is how we can have this stable knowledge when everything we sense is not stable.

E.g., if you observe two sticks, of (approximately) equal lengths, you know that they are equal, but by the same token, they are not perfectly equal.  Even if two material things are exactly equal, they are matching up to an ideal that exists apart from them: the Equal-itself.  The Equal-itself is what all instances of equal things have in common in virtue of which we say that they are equal.

Not only are mathematical Forms shared in by material things, but every Form which can be understood.  That is, whatever can be understood, and so is an object of knowledge, shares in some Form.  So there must be a Form for every species and attribute which things have in common, and by which they are understood.  So there is a Form of Oak-Tree-itself by which we recognize various material things as oaks, and oaks of various stages (acorn, sapling, adult tree) as stages of the same sort of thing.

Aristotle was interested in understanding material things in their very materiality and particularity, and so rejected Platonic Forms as immaterial, separate and unchanging realities to which mind had direct access (in opposition to sense perception).  Instead, Aristotle located the principle of intelligibility (which he continued to call forms) in the material things themselves.  Thus, each species, and each individual within that species, has its own form or essence, which not only allows the mind to understand these individuals (through the senses, not apart from them), but the forms are also the principles of action and of being.  A thing is an oak (acorn, sapling or tree) because it has one and the same internal principle (form (or in this case, soul)) which causes its matter to act as an oak, and so be an oak.  This same form allows mind to discover it is an oak by observing its actions through our senses.

2. Aquinas’ “Fourth Way” begins with a recognition of Transcendental Attributes

  • Transcendental Attributes are perfections which all things share in, in virtue of their being.
  • They are ‘convertible’ with being – each is a thing’s being in relation either to itself or other beings.
    • Being – the reality of a thing
      • Essence: what it is
      • Act of Existing: what makes it a real thing
    • One – the thing as undivided
    • Good – the thing as an object of desire
      • The perfection of its own being
      • The perfection of the being of another
    • True – the thing as an object of knowledge; the reality to which a mind conforms
    • Thing – being what it is (essence considered in itself)
    • Something – being other than everything else
    • Beautiful – perfection as an object of knowledge
  • Trancendentals are like Platonic Forms in that
    • they are shared in by material things more or less completely
    • they are the foundation of the reality and intelligibility of what shares in them (which is everything that is)
  • Transcendental Good (as Metaphysical Perfection)
    • Most obvious Transcendental Attribute in observable reality from which the Fourth Way proceeds (as another a posteriori proof)
    • Defined as ‘what each thing (truly) desires’ (should): the due good, or duly desirable
    • Not arbitrary or relativistic, because convertible with being
    • Each thing’s goodness is the perfection of its own being (metaphysical perfection)
      • A thing’s good is what is or contributes to its functioning well
      • This well-functioning is determined by the sort of thing it is, i.e., its nature or essence: what it is.
    • Incidentally, evil is the privation or lack of (a due) good.
      • Not every lack or privation is evil: unseeing rocks are not called blind, and do not suffer an evil.
      • Only what is supposed to see (and doesn’t) is called blind and suffers an evil
  • Relativistic Good
    • Alternative to objective good as metaphysical perfection
    • What is merely desirable
      • This is relative to what is desiring
        • An object of desire is good for something
        • No such thing as good absolutely
      • Arbitrary – not specified by anything beyond the desire (e.g. thing’s nature)
      • Correlative to competing interests of other things
        • What is good for one thing is evil for another
        • Non-absolute: no thing’s desire is privileged relative to other’s
    • ‘Evil’ is loss or thwarting of what is desired
  • Good and evil are mental/social constructs
    • A thing is ‘good’ only from perspective of what desires it
    • A thing is ‘evil’ only from the perspective of what dislikes it
    • Nothing is ‘good’ or ‘evil’ in itself
    • In themselves, events and things are metaphysically and morally neutral
  • Critique
    • The assertion about the relative nature of ‘good’ and ‘evil’ is intended to be regarded as an absolute or objective good
      • Metaphysical neutrality of values is true perspective, and one to be preferred (over absolutist perspective).
      • To believe in objective or metaphysical good/evil is objectively evil (mistaken) – it is a failure to adopt the true, relavistic perspective.
    • Therefore, the relativistic view of good and evil entails its denial, and so ultimately incoherent
    • Absurd consequences of maintaining relativistic view
      • Child rape, etc. not intrinsically evil
      • No fundamental human rights
      • World does not contain more evil than it should – everything that happens (tsunami’s, cancer, genocide, child rapists) happens just as it should (or cannot help but happen)

Aquinas’ Proof

The fourth way is taken from the gradation to be found in things.

a. Among beings there are some more and some less good, true, noble and the like.

The starting point of the proof is a recognition that there exists variations in transcendental attributes among real things.  For instance, within a given species of animal, some individuals manifest the attributes or functions characteristic of the species more or less perfectly.  It is certainly apparent that some individual dogs, e.g., may have a birth-defect or suffer a disability.  Such individuals as less-well-formed would be, by that fact, manifesting less of the perfection due (or ‘owed’) to that species.  And if individuals can be less perfect, others are more perfect.  These well-formed individuals would be more perfect, and to that extent and in this one respect, display greater metaphysical goodness (for a member of that species).

To recognize that some individuals more or less perfectly display the perfections of their species does not imply that any of them are perfect in all respects – that there is a perfect individual dog, for example.  Nor does it mean that dogs which display less of the perfection of a dog are morally bad dogs. Rather, to identify an individual as more or less perfect is to recognize that in some respect, e.g., running or barking for dogs, some individuals perform essential tasks better or worse.  Indeed, an individual dog may be imperfect in running ability, but excel in loyalty (and so be a ‘better’ dog than a four-legged mongrel).  Moreover, their doing this is a greater or lesser manifestation of what it is to be a member of that species, a greater or lesser display of their nature.  They all have the same nature (in being dogs), but that nature is more or less evident in each of them.  As a dog that cannot bark manifests its nature or being less perfectly, so, from this metaphysical perspective, its dog-ness or being is impeded; it is not all that a dog could be.  Likewise with individuals that exhibit more or greater characteristic behaviors or traits: some dogs manifest their dog nature more; they are being more of a dog.

Furthermore, just as individuals within a species may be more or less perfect, for Aquinas (as with most medieval thinkers) species themselves are more or less perfect to the extent that they do more, i.e., they display greater actuality, and actuality of a greater sort.  Amoebae and paramecia live a relatively simple life, do relatively little, and are relatively less perfect, at least compared to more complex life forms, worms, for instance.  They are thus relatively lesser beings because of their nature.  And as worms are more perfect than amoebae, so fish are more perfect than worms.  In all cases, the more perfect exhibit more being, and manifest greater metaphysical goodness.  So, then, living things, and all beings generally, fall on a scale of less to more perfect beings, less to more metaphysical goodness.

It is not necessary to construct the whole scale of being, and place every kind of thing in its precise relative location on that scale, in order to recognize that there is a scale.  By seeing the relative simplicity of worms compared to lions, one can see that things are more and less perfect, i.e. they have greater or less being.

b. But “more” and “less” are predicated of different things, according as they resemble in their different ways something which is the maximum,

i. as a thing is said to be hotter according as it more nearly resembles that which is hottest;

ii. so that there is something which is truest, something best, something noblest and, consequently, something which is uttermost being;

iii. for those things that are greatest in truth are greatest in being, as it is written in Metaph. ii.

To claim that things are more or less perfect implies that there is an ideal to which they more or less perfectly conform.  Aquinas terms this ‘ideal’ the ‘maximum.’  So, in order to recognize that a dog born with three legs is flawed or suffers a defect, one must implicitly acknowledge that four-leggedness is the ideal for dogs.  And, so with other attributes within a species.

So, as there is a ‘maximum’ or ideal to being a dog (since there are more and less perfect dogs), there is a ‘maximum’ or ideal to being simpliciter (i.e., in an absolute sense) since beings are more or less perfect.

c. Now the maximum in any genus is the cause of all in that genus; as fire, which is the maximum heat, is the cause of all hot things.

Each individual on the metaphysical scale of perfection at once manifests perfection, but that perfection is also at the same time limited; hence its position on the scale.  Aquinas thus argues that not only must there be an ideal or maximum of perfection, as there is with any gradation of attributes, something must also account for the variations in degrees of perfection in which things share.  That is, something other than the things themselves must have, as it were, ‘placed’ them on the scale, or be the cause of their having whatever perfection they have, and to whatever degree they have it.  It should be obvious, then, that the cause of the perfection of something which is placed on the scale cannot be itself on the scale, or have limited perfection, since its own placement or limitation would likewise need explanation.  Thus Aquinas concludes that the maximum is the cause of the gradation in perfection and of everything so graded.

d. Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection;

Just as the gradation in goodness or perfection is real, and must be caused by something which is goodness and perfection without limitation, so this unlimited good, perfect being is real.

e. and this we call God.

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