Meditations, Book 4, Section 4

Marcus Aurelius — The Emperor

If all people can understand and think clearly, then the reason that makes us rational is something we all share. If reason is universal, then the reason that tells us what to do and what not to do is also universal. If that's true, then law is universal. If law is universal, then we are all fellow citizens. If we're fellow citizens, then we share one common state. If that's true, then the world is like one big city. What other state could include every human being? From this shared city comes our understanding, our reason, and our law. Where else could they come from? Just as the earthy part of me comes from common earth, and the wet part comes from water, and my breath and life have their source — and the dry, fiery parts too (nothing comes from nowhere, and nothing disappears into nothing) — so my ability to understand comes from some shared beginning.

Marcus Aurelius — The Emperor Original

If to understand and to be reasonable be common unto all men, then is that reason, for which we are termed reasonable, common unto all. If reason is general, then is that reason also, which prescribeth what is to be done and what not, common unto all. If that, then law. If law, then are we fellow-citizens. If so, then are we partners in some one commonweal. If so, then the world is as it were a city. For which other commonweal is it, that all men can be said to be members of? From this common city it is, that understanding, reason, and law is derived unto us, for from whence else? For as that which in me is earthly I have from some common earth; and that which is moist from some other element is imparted; as my breath and life hath its proper fountain; and that likewise which is dry and fiery in me: (for there is nothing which doth not proceed from something; as also there is nothing that can be reduced unto mere nothing:) so also is there some common beginning from whence my understanding hath proceeded.