It is clear that we must obtain knowledge of the primary causes, because it is when we think that we understand its primary cause that we claim to know each particular thing. Now there are four recognized kinds of cause. Of these we hold that one is the essence or essential nature of the thing (since the “reason why” of a thing is ultimately reducible to its formula, and the ultimate “reason why” is a cause and principle); another is the matter or substrate; the third is the source of motion; and the fourth is the cause which is opposite to this, namely the purpose or “good”; for this is the end of every generative or motive process. We have investigated these sufficiently in the Physics¹; 983bhowever, let us avail ourselves of the evidence of those who have before us approached the investigation of reality and philosophized about Truth. For clearly they too recognize certain principles and causes, and so it will be of some assistance to our present inquiry if we study their teaching; because we shall either discover some other kind of cause, or have more confidence in those which we have just described. Most of the earliest philosophers conceived only of material principles as underlying all things. That of which all things consist, from which they first come and into which on their destruction they are ultimately resolved, of which the essence persists although modified by its affections—this, they say, is an element and principle of existing things. Hence they believe that nothing is either generated or destroyed, since this kind of primary entity always persists. Similarly we do not say that Socrates comes into being absolutely when he becomes handsome or cultured, nor that he is destroyed when he loses these qualities; because the substrate, Socrates himself, persists. In the same way nothing else is generated or destroyed; for there is some one entity (or more than one) which always persists and from which all other things are generated. All are not agreed, however, as to the number and character of these principles. Thales,² the founder of this school of philosophy,³ says the permanent entity is water (which is why he also propounded that the earth floats on water). Presumably he derived this assumption from seeing that the nutriment of everything is moist, and that heat itself is generated from moisture and depends upon it for its existence (and that from which a thing is generated is always its first principle). He derived his assumption, then, from this; and also from the fact that the seeds of everything have a moist nature, whereas water is the first principle of the nature of moist things. There are some⁴ who think that the men of very ancient times, long before the present era, who first speculated about the gods, also held this same opinion about the primary entity. For they⁵ represented Oceanus and Tethys to be the parents of creation, and the oath of the gods to be by water— Styx,⁶ as they call it. Now what is most ancient is most revered, and what is most revered is what we swear by. 984aWhether this view of the primary entity is really ancient and time-honored may perhaps be considered uncertain; however, it is said that this was Thales’ opinion concerning the first cause. (I say nothing of Hippo,⁷ because no one would presume to include him in this company, in view of the paltriness of his intelligence.) Anaximenes⁸ and Diogenes⁹ held that air is prior to water, and is of all corporeal elements most truly the first principle. Hippasus¹⁰ of Metapontum and Heraclitus¹¹ of Ephesus hold this of fire; and Empedocles¹²—adding earth as a fourth to those already mentioned—takes all four. These, he says, always persist, and are only generated in respect of multitude and paucity, according as they are combined into unity or differentiated out of unity.¹³ Anaxagoras of Clazomenae—prior to Empedocles in point of age, but posterior in his activities—says that the first principles are infinite in number. For he says that as a general rule all things which are, like fire and water,¹⁴ homoeomerous, are generated and destroyed in this sense only, by combination and differentiation; otherwise they are neither generated nor destroyed, but persist eternally.¹⁵ From this account it might be supposed that the only cause is of the kind called “material.” But as men proceeded in this way, the very circumstances of the case led them on and compelled them to seek further; because if it is really true that all generation and destruction is out of some one entity or even more than one, why does this happen, and what is the cause? It is surely not the substrate itself which causes itself to change. I mean, e.g., that neither wood nor bronze is responsible for changing itself; wood does not make a bed, nor bronze a statue, but something else is the cause of the change. Now to investigate this is to investigate the second type of cause: the source of motion, as we should say. Those who were the very first to take up this inquiry, and who maintained that the substrate is one thing, had no misgivings on the subject; but some of those¹⁶ who regard it as one thing, being baffled, as it were, by the inquiry, say that that one thing (and indeed the whole physical world) is immovable in respect not only of generation and destruction (this was a primitive belief and was generally admitted) but of all other change. This belief is peculiar to them. 984bNone of those who maintained that the universe is a unity achieved any conception of this type of cause, except perhaps Parmenides¹⁷; and him only in so far as he admits, in a sense, not one cause only but two.¹⁸ But those who recognize more than one entity, e.g. hot and cold, or fire and earth, are better able to give a systematic explanation, because they avail themselves of fire as being of a kinetic nature, and of water, earth, etc., as being the opposite.¹⁹ After these thinkers and the discovery of these causes, since they were insufficient to account for the generation of the actual world, men were again compelled (as we have said) by truth itself to investigate the next first principle. For presumably it is unnatural that either fire or earth or any other such element should cause existing things to be or become well and beautifully disposed; or indeed that those thinkers should hold such a view. Nor again was it satisfactory to commit so important a matter to spontaneity and chance. Hence when someone²⁰ said that there is Mind in nature, just as in animals, and that this is the cause of all order and arrangement, he seemed like a sane man in contrast with the haphazard statements of his predecessors.²¹ We know definitely that Anaxagoras adopted this view; but Hermotimus²² of Clazomenae is credited with having stated it earlier. Those thinkers, then, who held this view assumed a principle in things which is the cause of beauty, and the sort of cause by which motion is communicated to things.

It might be inferred that the first person to consider this question was Hesiod, or indeed anyone else who assumed Love or Desire as a first principle in things; e.g. Parmenides. For he says, where he is describing the creation of the universe, Love sheProbably Aphrodite (so Simplicius, Plutarch). created first of all the gods . . .²³And Hesiod says,²⁴ First of all things was Chaos made, and then/Broad-bosomed Earth . . ./And Love, the foremost of immortal beings, thus implying that there must be in the world some cause to move things and combine them. The question of arranging these thinkers in order of priority may be decided later. Now since it was apparent that nature also contains the opposite of what is good, i.e. not only order and beauty, but disorder and ugliness; 985aand that there are more bad and common things than there are good and beautiful: in view of this another thinker introduced Love and Strife²⁵ as the respective causes of these things— because if one follows up and appreciates the statements of Empedocles with a view to his real meaning and not to his obscure language, it will be found that Love is the cause of good, and Strife of evil. Thus it would perhaps be correct to say that Empedocles in a sense spoke of evil and good as first principles, and was the first to do so—that is, if the cause of all good things is absolute good. These thinkers then, as I say, down to the time of Empedocles, seem to have grasped two of the causes which we have defined in the Physics²⁶: the material cause and the source of motion; but only vaguely and indefinitely. They are like untrained soldiers in a battle, who rush about and often strike good blows, but without science; in the same way these thinkers do not seem to understand their own statements, since it is clear that upon the whole they seldom or never apply them. Anaxagoras avails himself of Mind as an artificial device for producing order, and drags it in whenever he is at a loss to explain some necessary result; but otherwise he makes anything rather than Mind the cause of what happens.²⁷ Again, Empedocles does indeed use causes to a greater degree than Anaxagoras, but not sufficiently; nor does he attain to consistency in their use. At any rate Love often differentiates and Strife combines: because whenever the universe is differentiated into its elements by Strife, fire and each of the other elements are agglomerated into a unity; and whenever they are all combined together again by Love, the particles of each element are necessarily again differentiated. Empedocles, then, differed from his predecessors in that he first introduced the division of this cause, making the source of motion not one but two contrary forces. Further, he was the first to maintain that the so-called material elements are four—not that he uses them as four, but as two only, 985btreating fire on the one hand by itself, and the elements opposed to it—earth, air and water—on the other, as a single nature.²⁸ This can be seen from a study of his writings.²⁹ Such, then, as I say, is his account of the nature and number of the first principles. Leucippus,³⁰ however, and his disciple Democritus³¹ hold that the elements are the Full and the Void—calling the one “what is” and the other “what is not.” Of these they identify the full or solid with “what is,” and the void or rare with “what is not” (hence they hold that what is not is no less real than what is,³² because Void is as real as Body); and they say that these are the material causes of things. And just as those who make the underlying substance a unity generate all other things by means of its modifications, assuming rarity and density as first principles of these modifications, so these thinkers hold that the “differences”³³ are the causes of everything else. These differences, they say, are three: shape, arrangement, and position; because they hold that what is differs only in contour, inter-contact, and inclination .³⁴(Of these contour means shape, inter-contact arrangement, and inclination position.) Thus, e.g., A differs from N in shape, AN from NA in arrangement, and Z from N³⁵ in position. As for motion, whence and how it arises in things, they casually ignored this point, very much as the other thinkers did. Such, then, as I say, seems to be the extent of the inquiries which the earlier thinkers made into these two kinds of cause.