Its importance is indeed very great, since it may truly be called the basis of all science. For by _science_ we understand a _system_ of notions, _i.e._ a totality of connected, as opposed to a mere aggregate of disconnected, notions. But what is it that binds together the members of a system, if not the Principle of Sufficient Reason? That which distinguishes every science from a mere aggregate is precisely, that its notions are derived one from another as from their reason. So it was long ago observed by Plato: καὶ γὰρ αἱ δόξαι αἱ ἀληθεῖς οὐ πολλοῦ ἄξιαί εἰσιν, ἕως ἄν τις ἀυτὰς δήσῃ αἰτίας λογισμῷ (_etiam opiniones veræ non multi pretii sunt, donec quis illas ratiocinatione a causis ducta liget_).[13] Nearly every science, moreover, contains notions of causes from which the effects may be deduced, and likewise other notions of the necessity of conclusions from reasons, as will be seen during the course of this inquiry. Aristotle has expressed this as follows: πᾶσα ἐπιστήμη διανοητική, ἢ καὶ μετέχουσά τι διανοίας, περὶ αἰτίας καὶ ἀρχάς ἐστι (_omnis intellectualis scientia, sive aliquo modo intellectu participans, circa causas et principia est_).[14] Now, as it is this very assumption _à priori_ that all things must have their reason, which authorizes us everywhere to search for the _why_, we may safely call this _why_ the mother of all science. [13] "Meno." p. 385, ed Bip. "Even true opinions are not of much value until somebody binds them down by proof of a cause." [Translator's addition.] [14] Aristot. "Metaph." v. 1. "All knowledge which is intellectual or partakes somewhat of intellect, deals with causes and principles." [Tr.'s add.] § 5. _The Principle itself._ We purpose showing further on that the Principle of Sufficient Reason is an expression common to several _à priori_ notions. Meanwhile, it must be stated under some formula or other. I choose Wolf's as being the most comprehensive: _Nihil est sine ratione cur potius sit, quam non sit._ Nothing is without a reason for its being.[15] [15] Here the translator gives Schopenhauer's free version of Wolf's formula. CHAPTER II. GENERAL SURVEY OF THE MOST IMPORTANT VIEWS HITHERTO HELD CONCERNING THE PRINCIPLE OF SUFFICIENT REASON. § 6. _First Statement of the Principle and Distinction between Two of its Meanings._