In the "Analyt. post." i. 2, Aristotle states the principle of sufficient reason to a certain degree when he says: ἐπίστασθαι δὲ οἰόμεθα ἕκαστον ἁπλῶς, ὅταν τὴν τ' αἰτίαν οἰόμεθα γινώσκειν, δι' ἣν τὸ πρᾶγμα ἔστιν, ὅτι ἐκείνου αἰτία ἐστίν, καὶ μὴ ἐνδέχεσθαι τοῦτο ἄλλως εἶναι. (_Scire autem putamus unamquamque rem simpliciter, quum putamus causam cognoscere, propter quum res est, ejusque rei causam esse, nec posse eam aliter se habere._)[19] In his "Metaphysics," moreover, he already divides causes, or rather principles, ἀρχαί, into different kinds,[20] of which he admits eight; but this division is neither profound nor precise enough. He is, nevertheless, quite right in saying, πασῶν μὲν οὖν κοινὸν τῶν ἀρχῶν, τὸ πρῶτον εἶναι, ὅθεν ἢ ἔστιν, ἢ γίνεται, ἢ γιγνώσκεται.[21] (_Omnibus igitur principiis commune est, esse primum, unde aut est, aut fit, aut cognoscitur._) In the following chapter he distinguishes several kinds of causes, although somewhat superficially and confusedly. In the "Analyt. post." ii. 11, he states four kinds of causes in a more satisfactory manner: αἰτίαι δὲ τέσσαρες· μία μὲν τό τι ἦν εἶναι· μία δὲ τὸ τινῶν ὄντων, ἀνάγκη τοῦτο εἶναι· ἑτέρα δὲ, ἥ τι πρῶτον ἐκίνησε· τετάρτη δὲ, τὸ τίνος ἕνεκα.[22] (_Causæ autem quatuor sunt: una quæ explicat quid res sit; altera, quam, si quædam sint, necesse est esse; tertia, quæ quid primum movit; quarta id, cujus gratia._) Now this is the origin of the division of the _causæ_ universally adopted by the Scholastic Philosophers, into _causæ materiales, formales, efficientes et finales_, as may be seen in "Suarii disputationes metaphysicæ"[23]--a real compendium of Scholasticism. Even Hobbes still quotes and explains this division.[24] It is also to be found in another passage of Aristotle, this time somewhat more clearly and fully developed ("Metaph." i. 3.) and it is again briefly noticed in the book "De somno et vigilia," c. 2. As for the vitally important distinction between _reason_ and _cause_, however, Aristotle no doubt betrays something like a conception of it in the "Analyt. post." i. 13, where he shows at considerable length that knowing and proving _that_ a thing exists is a very different thing from knowing and proving _why_ it exists: what he represents as the latter, being knowledge of the _cause_; as the former, knowledge of the _reason_. If, however, he had quite clearly recognized the difference between them, he would never have lost sight of it, but would have adhered to it throughout his writings. Now this is not the case; for even when he endeavours to distinguish the various kinds of causes from one another, as in the passages I have mentioned above, the essential difference mooted in the chapter just alluded to, never seems to occur to him again. Besides he uses the term αἴτιον indiscriminately for every kind of cause, often indeed calling reasons of knowledge, and sometimes even the premisses of a conclusion, αἰτίας, as, for instance, in his "Metaph." iv. 18; "Rhet." ii.