Hume.

Hume; being an empiricist, believed that we can only attain knowledge from what we experience through our senses. He therefore centres the existence of the world around sense data. Through his "Bundle theory", he claims that objects don't exist within themselves, but rather through their properties. An apple (cliched as an example as it is) is red, round and potentially sweet. If said apple was stripped of these properties (which are determined by sense data) the apple would in fact no longer exist. This therefore can also be applied to humans and our very own existence can be put into question.
The problem of the induction fallacy follows that no assumptions can be made about  future events simply because they  happened to take place in the past. You can not state that all swans are white because that is all you've encoured as you might  just cross one of a different colour (Imagine how silly they felt when a black swan was discovered). This is a problem for scientific theory as science claims that one can draw conclusions about an event if it can be reproduced repeatedly.
The Treatise of Human nature is divided into three books, dealing effectively with The Understanding, The Passions, and The ideas. He stated the distinction between two kinds of perceptions; the impressions and the ideas, impressions being more forceful and violent than the fainter notion of ideas. According to him, simple ideas have simple impressions as the former are derived from the latter. Complex ideas however, need not resemble impressions, as their contents instead are derived from a mixture of impressions.