By refuting empiricism, the preceding lecture established that individual experience alone can't explain rational judgments. But recently a new version of empiricism has appeared – one that escapes the objections we've just made. According to this new doctrine, rational judgments are innate but derive from the experience of the species. The first ideas attributed to reason aren't constructed de novo in the mind of each human being but – together with their derivative judgments – are there already formed. Their presence, however, can be explained as a kind of trust, made up of the accumulated experience of the species. Recognizing that many things are transmitted by heredity from ancestors to their descendants, this doctrine explains all of knowledge in this way. Reason thus might be defined as the totality of hereditary knowledge.

This theory of the origins of reason is part of the broader hereditary theory, which itself is but one chapter of the famous doctrine that follows from Darwin's hypothesis – evolutionism. The greatest philosophical champion of this doctrine is Herbert Spencer, who extended it from its original domain – natural history – to philosophy. The general exposition of his system is contained in his First Principles.

To better judge the value of hereditary theory as applied to the origins of reason, let's examine the fundamental principles of evolutionism.