" The less forcible and lively are commonly referred to as "thoughts/ideas", while "impressions" are more lively perceptions of "what we hear, see, feel, love, hate, desire, or will" (Hume 10). Hume further claims that all our ideas are merely copies of our impressions. To back up this claim, he suggests that all our complex ideas (Example- our idea of God) are derived from simple ideas, which in turn, are copied from a sentiment or feeling. To explain this concept, Hume remarks that the idea of God as intelligent, wise, and a good being just arises when we reflect on our own virtues and augment them without a limit to infinity. Additionally, he also proposes that our imagination is only derived from what we have impressions of. Therefore, a blind man is never able to see colors or a man of mild manners can never imagine cruelty. In order to understand the meaning of any idea, it has to be traced back to the original feeling/sentiment. Even when an idea at first seems completely wild and excursive, there is always a principle of connection between all ideas of the mind. The three main principles to explain this connection are resemblance, contiguity in place or time, and cause and effect. .
Central to the understanding of human nature are two propositions of "relations of ideas" and "matters of fact." "Relations of ideas" can be discovered by "mere operations of thought" are as a result, are "intuitively and demonstratively certain" (Hume 15). For example, a2 + b2 = c2 can be easily discovered by a priori knowledge. "Matters of fact," on the other hand, are learned a posteriori and all "reasoning concerning matters of fact seem to be founded on the relation of "cause and effect" (Hume 16). Additionally, the knowledge of relation of cause and effect is discoverable, not by reason, but by experience when we find constant conjunction between particular objects.
