Diogenes Laërtius,
Lives of the Eminent Philosophers…
(1925)
“ Hence it is from plain facts that we must start when we draw inferences about the unknown. [47] For all our notions are derived from perceptions, either by actual contact or by analogy, or resemblance, or composition, with some slight aid from reasoning. And the objects presented to mad-men [48] and to people in dreams are true, for they produce effects – i.e. movements in the mind – which that which is unreal never does.33. By preconception they mean a sort of apprehension or a right opinion or notion, or universal idea stored in the mind ”
