David Hume

“ The essence and composition of external bodies are so obscure, that we must necessarily, in our reasoning's, or rather conjectures conceding them, involve ourselves in contradictions and absurdities. But as the perceptions of the mind are perfectly known, and I have us'd all imaginable caution in forming conclusions conceding them, I have always hop'd to keep clear of those contradictions, which have attended every other system. ”

“ The passions of love and hatred are always followed by, or rather conjoin'd with benevolence and anger. 'Tis this conjunction, which chiefly distinguishes these affections from pride and humility. For pride and humility are pure emotions in the soul, unattended with any desire, and not immediately exciting us to action. ”

“ Ideas may be compar'd to the extension and solidity of matter, and impressions, especially reflective ones, to colours, tastes, smells and other sensible qualities. Ideas never admit of a total union, but are endow'd with a kind of impenetrability, by which they exclude each other, and are capable of forming a compound by their conjunction, not by their mixture. ”

“ We may, therefore, infer, that benevolence and anger are passions different from love and hatred, and only conjoin'd with them, by the original constitution of the mind. As nature has given to the body certain appetites and inclinations, which she encreases, diminishes, or changes according to the situation of the fluids or solids ”