As far as possible we ought to try and reduce all that we wish to incorporate in our memory to a perceptible image, either directly, or as an example, a mere simile, or an analogue, or indeed in any other way; because intuitive perceptions take a far firmer hold than any abstract thoughts, let alone mere words. This is why we remember things we have ourselves experienced so much better than those of which we read. CHAPTER VIII. GENERAL OBSERVATIONS AND RESULTS. § 46. _The Systematic Order._ The order of succession in which I have stated the various forms of the Principle of Sufficient Reason in this treatise, is not systematic; it has been chosen for the sake of greater clearness, in order first to present what is better known and least presupposes the rest. In this I have followed Aristotle's rule: καὶ μαθήσεως οὐκ ἀπὸ τοῦ πρώτου, καὶ τῆς τοῦ πράγματος ἀρχῆς ἐνίοτε ἀρκτέον, ἀλλ' ὅθεν ῥᾷστ' ἂν μάθοι (_et doctrina non a primo, ac rei principio aliquando inchoanda est, sed unde quis facilius discat_).[156] But the systematic order in which the different classes of reasons ought to follow one another is the following. First of all should come The Principle of Sufficient Reason of Being; and in this again first its application to Time, as being the simple schema containing only what is essential in all the other forms of the Principle of Sufficient Reason, nay, as being the prototype of all finitude. The Reason of Being in Space having next been stated, the Law of Causality would then follow; after which would come the Law of Motives, and last of all the Principle of Sufficient Reason of Knowing; for the other classes of reasons refer to immediate representations, whereas this last class refers to representations derived from other representations. [156] Aristot. "Metaph." iv. 1. "Sometimes too, learning must start, not from what is really first and with the actual beginning of the thing concerned, but from where it is easiest to learn." [Tr.'s add.]