  Strang 1963 proposes a solution to the problem. While acknowledging that there can never be pure instances of any ingredient in actuality, there could be such instances in analysis. I can analyze mixtures and determine predominant ingredients, but I will never be able to produce a pure instance of such an ingredient.  The problem here is how this would be worked out, and why I can be certain that there are such natures (as we might call them).  Anaxagoras suggests two things. First, in B12 he stresses that nous has the power to know and understand all the ingredients (indeed cosmic nous apparently knew all this before the rotation began; see quotation above). Second, in B21 and B21a he suggests how human nous (nous in us) can come to such an understanding by relying on sense perception but moving beyond it in thought (see sect. 5. Knowledge). Finally, because the ingredients are genuinely basic entities in the sense required to ground a rational cosmology in the Eleatic sense, they must be stable natures in the Parmenidean sense (for a related account, see Marmodoro 2015). Anaxagoras is committed to the arguments that ground Eleatic metaphysics; thus he can claim an a priori reason to think that the ingredients can be knowable in the sense required by the Principle of Predominance.  His epistemological view that humans can reach understanding through beginning with sense experience then fits with these metaphysical commitments.