Diogenes Laertius

Therefore, this path must be followed, and thereafter constant effort must be applied to cultivating the memory so that attention to things themselves becomes steady and easy. From these forms of things, or from generally understood notions fixed in the mind, one can find the answer when something specific must be investigated. This is done by weighing the matter according to first principles and the words used to explain them. Indeed, when such steadiness and ease are prepared, and the mind is equipped with refined, general information, it becomes possible to perceive quickly whatever one wishes. I say meanwhile also according to words since it is impossible for a coherent summary of general headings to be frequently repeated in the memory unless it contains everything in a way that can be explained in a few words; this applies even when something has been specifically explored. Consequently, since this way of acting is most useful to those who are natural students of Natural Philosophy original: "Physiologiæ"; in this context, the study of the physical world and its laws and devoted to it, I would advise them to undertake such labor in Natural Philosophy. This is especially true if they enjoy a tranquil way of life, so that they might also prepare for themselves such an Epitome A brief summary or abstract of a larger work of general opinions and an outline of information by primary headings.

First then, O Herodotus, one must diligently hold onto the meanings underlying words, or what words signify, so that we may have a point of reference. By looking back to these, we can safely judge whatever we may think, seek, or doubt. Otherwise, while everything passes by us unjudged, those who demonstrate something to us might proceed without limit, and we would receive nothing but empty voices or the mere sound of words. For it is necessary that we look toward that primary notion or meaning for which any word is used, and that its perception requires no demonstration; this is essential if we are to have a reference point for what is sought, doubted, or thought. Next, one must explore all things either through the Senses themselves, or through direct inspections made by the mind or any of the criteria The standards or rules used to judge truth, or finally through the resulting passions original: "passiones"; the internal feelings of pleasure or pain used to make choices. This is necessary so that we have a basis from which to draw a conjecture, both regarding that which is called The Thing Awaited original: "Prosphenomenon seu exspectabile"; an object of perception that requires closer observation to confirm its nature (as if there is hope that it may one day be known more clearly through itself) and regarding that which is unmanifest by its own nature and can only be known through something else. But having set these aside, we must proceed to consider those things that are unmanifest in this way.

And first of all, it seems established that nothing comes from nothing, and nothing passes away into nothingness. For if something were created out of nothing, anything could be born from anything, surely having no need for seeds. And if that which perishes fell into nothingness, all things...

Therefore, one must proceed and continuously work on the memory to such an extent that the most important grasp of things is achieved. Indeed, every specific detail can be found once the most general patterns are embraced and remembered. (Since for the person who has reached perfection, the most important thing, and the precision of the whole, becomes the ability to use these grasps quickly) or by reducing them to simple elements and words. For it is not possible to have a condensed understanding of the continuous circuit of the whole unless one is able to include everything within oneself through brief words, including what has been precisely investigated in detail. Hence, since such a path is useful to those who are accustomed to Natural Philosophy, I recommend continuous activity in Natural Philosophy—especially for those who bring peace to their lives—by making some such summary and elementary outline of all doctrines.

First then, Herodotus, one must grasp the things underlying sounds original: "τοῖς φθόγγοις"; the fundamental meanings of spoken words, so that we may have a point of reference to which we can refer our opinions, inquiries, or doubts in order to judge them. Otherwise, everything will be undecided for us as we demonstrate things to infinity, or we will have only empty sounds. For it is necessary that the first concept associated with each sound be seen and require no demonstration, if we are to have a target to which we refer the thing sought, doubted, or thought. Then, one must observe everything according to the senses, and simply according to the present grasps, whether of the mind or any of the criteria. Likewise, one must observe according to existing feelings, so that we may have the means to signpost both what is awaited and what is unmanifest. Once these things are distinguished, one must look together at the things that are unmanifest.

First, that nothing comes into being from what is not, and nothing is destroyed into what is not. For if that which appears came into being from what is not, everything would come into being from everything, having no need for seeds. And if that which disappears were destroyed into what is not, all things...