Hume

Along the same line of Pascal and Berkeley, David Hume (Edinburgh, 1711 – 1776) believes that the interest of philosophy should be directed towards human nature, compared to the previous philosophy, which instead sought to understand the world. Like Berkeley, he states that what we perceive is only a bundle of sensations that nothing authorizes us to refer back to objects that would be the source. Our mind does nothing but associate, aggregate, look for similarities, and so imagine the existence of an objective world, creating to itself ideas of particular objects . When we return to observe an object after a certain time, our imagination provides to fill the observation gap, assuming that that object has continued to have its own existence even when we did not look at it.
Universal concepts are nothing but a fruit of our memory, of our habit of noticing certain similarities between some similar objects; actually no human being is able to think of purely universal ideas: the moment they believe they are doing it, they do nothing but remember many particular similar ideas that they thought of during their existence. The same criticism applies to the concepts of cause and effect: we think we understand its meaning because we have become accustomed, over time, to associating certain consecutive phenomena, which occur one after the other, but actually nothing authorizes us to think that the phenomenon that occurs first is really the cause of what occurs immediately afterwards.
Hume also extends these concepts to our perception of being “I”: we too are nothing but bundles of impressions that our mind associates, aggregates, deciding to refer them back to a single “I”, which would be at their base. We, that is the “I”, are instead something like a theater, where impressions and ideas continually pass and repass. This theater, however, is to be conceived not as a stable building, but simply as the passing and repassing of impressions itself. We have no proof, actually, of the existence of such theater.

We can consider this conception as a strong criticism against Descartes. He had said “I think, therefore I am”; Hume would say “I think, therefore my thoughts exist”. Nothing allows me to conclude that, behind these thoughts, there is an “I” who hosts them; it is just an imagination of ours, which we have no chance of demonstrating. In relation to this way of thinking, according to Hume there is no freedom; freedom it is a meaningless concept.