Methodology of psychology
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The nature of mind is demonstrated only by introspection.
He that is to govern a whole nation must read in himself, not this, or that particular man; but mankind: which though it be hard to do, harder than to learn any language or science; yet, when I shall have set down my own reading orderly and perspicuously, the pains left another will be only to consider if he also find not the same in himself. For this kind of doctrine admitteth no other demonstration.
Hobbes, Lev Intro. 4