David Hume

Impressions and Ideas
David Hume is a skeptic, he believes we have no reason to be certain about anything. Similarly to Hobbes and Locke, Hume is an empiricist, he believes our knowledge is derived from our senses; things that we see, hear, taste, touch and smell on the outside. He classifies all that we can see and touch etc as 'impressions', and it is these impressions which connect information to our minds which combine to form ideas.
Impressions = sensations, passions and emotions
Ideas = faint images of our impressions in thought
Hume believes our brain was empty apart from all the impressions that have sunk in from the outside world.

But, can we always trust these ideas? Hume says NO.

Hume questions the basis of all our beliefs, he believes that we have no reason to be 100% certain, for instance whether the sun will rise tomorrow can not be guaranteed. This leads on to his theory on causation.

Causation 
Causation is the relationship between two or more events, one which follows as a result of the other. Hume disagrees with causation, he believes that is it wrong to think one thing can follow another, he expresses that it could be 'probable' and we can work it out through inductive reasoning, but nothing can be for certain. The example used in HWP is of an apple; how do you know that your apple won't taste like roast beef next time? He persists that just because something has happened before, it does not mean it will happen again. In this case you cannot guarantee what the apple will taste like in the future, even though you are familiar with the taste of the apples you have eaten in the past. Hume states that there is no casual connection between two objects, our minds just conjoin the two. I'm sure Hume would adopt the famous words "expect the unexpected", as he believes that our mind tricks us into thinking that one thing causes another. For instance, when you turn the tap on you expect water to come out, how do you know that custard won't come out of it tomorrow?

The very first cause was God, he is at the top of the long chain of causes. He set the cause in motion but played no further role.
The ontological proof of the existence of god -To doubt the existence of God means to doubt the first cause, because if there was no first cause then the universe would not exist. Therefore God must exist.

Induction
There are two types of logic:
1. Analytic Logic (Deductive Logic) - this is logic which is true by definition e.g all bicycles have two wheels
2. Synthetic Logic (Induction Logic) - this is the opposite to analysis, it is true by observation/verification. It is about building things up. e.g The cat is on the mat

Bundle Theory
Hume's Bundle Theory is the idea that an object such as an apple is made up of a collection of properties. For example, when you think of an apple immediately its properties such as its colour and shape spring to mind. Hume also suggests that the 'self' is merely a bundle of perceptions too.

A final note to end on:
Hume's Law: "You cannot derive an ought from an is" this is stated in his book 'Treatise of Human Nature'. This is the idea that we cannot say something "ought" to be, it either is or it isn't. This supports his belief that nothing is for certain.