I'm not sure there's any short quote that summarizes it. But as I read him, thought is composed of ideas, which are themselves "no more than the compounding, t

I'm not sure there's any short quote that summarizes it. But as I read him, thought is composed of ideas, which are themselves "no more than the compounding, transposing, augmenting, or diminishing" of other ideas. And ideas are very simple things, fundamentally based on impresseions like awareness of the colour red or of pain. And these ideas relate to each other in terms of "only three Principles of Connexion among Ideas, viz. Resemblance, Contiguity in Time or Place, and Cause or Effect". I think equating his 'ideas' with perceptrons might be anachronistic. But it does seem to suggest complex and abstract ideas are composites, built of networks of networks of simpler ideas, the connections between them being of a simple nature as well, perhaps all boiling down to nothing more than many stacked layers of basic sensations being present or absent, plus how they are sequenced and associated. It's not completely revolutionary; much of it follows Aristotle. The particular emphasis on 'ideas' and their 'connexions' being everything to thought, is perhaps original to Hume. This is in essays 2 and 3. Makes me think of Leucippus and his atoms. Not really our atoms, and yet still uncanny in their resemblance, especially with so little to go on. Disclaimer: I haven't read it in some 20 years besides skimming for the above quotes, and I'm not a philosopher.