The observation that oil and water do not mix, as pointed out by Empedocles (450BC), has led to much philosophical discussion, e.g. Aristotle (330BC), Goethe (1809), Mimkes (2005), to name a few examples, particularly in respect to the observation that certain groups, faiths, or types of people do not mix.

“Empedocles, then, thinks that sense-perception and thinking occur thus; but from what he says one might wonder first of all how ‘living things’ differ from ‘other things’ with respect to sense-perception. For things fit into the pores of ‘lifeless things’ too; for in general he says that mixture occurs by a symmetry of pores. That is why oil and water do not mix [N1], but other fluids do, as indeed do other substances whose proper blends he lists. Consequently, everything will perceive and mixture, sense-perception, and growth will be the same process. For he makes them all [occur] by the symmetry of pores, unless he add some differentiating feature.”

— Author (c.300BC), “Testimonia #12”, in: The Poem of Empedocles (pg. 198) [1]

“[Empedocles] claimed that there is a mixture and blending of those things whose solid parts and pores (i.e. hollows and dense parts) are symmetrical; for example, water and wine. But he claimed that things in which they are asymmetrical are unmixed, for example oil and water. Fore he says that ‘water is more easily fitted to wine, but with oil it does not want [to mix].’ (89/91). He says this about every body and gives it as the cause of the sterility of mules.”

— Philoponus (c.550), Commentary on Aristotle’s De Generatione Animalium CIAG 14.3, 123.16-21; “CTXT-78” in: The Poem of Empedocles (pg. 133) [1]

“I am standing here in the name of the human reason common to us all, and in the name of that human reason, I repeat, it is not the question of ‘Rome and Reason’ The question is, and will ever be, ‘Rome or Reason,’ as long as Rome will not, like MacMahon, submit; as long as Rome will still try to subdue and enslave Reason; as long as the Roman Catholic Church will understand the issue of ‘Rome and Reason’ only in the sense in which oil combines with water—whatever the poor water may do the oil is always at the top. As long as the Roman Catholic Church claims to be the oil whence all the light comes, and that the poor water is only quenching that light, then there will be no question whatever to me, or to a great many others, that the ways of Rome are altogether other ways than the ways of Reason.”

— S.H. Sonneschein (1878), “Review of Bishop Ryan’s Lecture on Catholicism” [3]