David Hume 1711-76

Hume wrote his “Treatise on Human Nature” between 1734 and 1737. He then shortened it, leaving out most of his reasons for his conclusions, in his “Inquiry Into Human Understanding”. This was said to be the book which awakened Kant from his “dogmatic slumbers”. His “Treatise on Human Nature” was split into three books concerning:
1) Understanding
2) Passions
3) Morals

The first book is where Hume draws the distinction between “impressions” and “ideas”.  Impressions are the direct products of immediate experience, whereas ideas are the faint copies of these impressions. Simple ideas resemble simple impressions, but complex ideas need not. For example we can imagine a winged horse without having seen one, but the constituents of this idea (the horse, the wings) are derived from sensory impressions. Another example is the “Golden Mountain”, we can imagine a golden mountain without having ever seen one. If you have had a sensory experience of gold, and a sensory experience of a mountain, then you can have a conglomeration of those sensory experiences, to imagine a “golden mountain”.
The logical objection is when we find resemblance among several objects and apply the same name to all of them, such as “wardrobe”. The psychological objection is known as the issue of vagueness, which comes from the part of the theory which states ideas are copies of impressions. For example if you were to see a 6ft tall man, your image of him may not be exact in that you may imagine him a few inches smaller, or taller, than his actual size. Hume argues that what is actually represented isn’t psychologically true. Like Berkley, Hume also banished the concept of substance from his philosophy. Hume argues that you cannot know the “self” as it is merely a bundle of perceptions and you cannot perceive the “thing” in itself. However this does not mean there is no “self”, it just means we cannot be certain whether there is or not.

In Hume’s section “Of Knowledge and Probability” probable knowledge is defined as uncertain knowledge, which is gained by inference and is not empirically demonstrative, e.g. knowledge of the future. Basically probable knowledge is everything except direct observation, logic or mathematics. Hume distinguished that there are seven categories of thinking:
1)Resemblance
2) Identity
3)Relations of Time and Space
4) Proportion in Quality and Number
5) Degrees in any quality
6) Contrariety
7) Causation

Hume argues that there is no such thing as an impression of causal relation. Cartesian and Scholastic philosophers stated that cause and effect is necessary and logical. Hume refuted this and stated that all we know of cause and effect is from sensory experience. But knowledge of causation doesn’t come from just one instance, it is requires the constant conjunction of one thing to another (of A to B).  Hume stated that when we say “A causes B” we only mean that A and B are conjoined by fact, there is no necessity that A be conjoined to B. Just because in our experience A and B always appear together or in rapid succession, this is no reason to expect them to be conjoined in the future. This is the argument that you cannot derive an “ought” from an “is”. The fact that the sun has risen every morning until now, this does not necessarily mean that the sun will rise tomorrow. The frequent conjunction of A and B gives us no reason to expect them to be conjoined in the future, our inclination to expect this is explained by the laws of habit and of association.

Hume also looks into the concept of miracles and he argues that you cannot believe in miracles until you have experienced them, knowledge requires empirical evidence. “Extraordinary claims require extraordinary proof”.