Locke considered that knowledge could be of certain types depending on how ideas could be compared. The idea of black, for instance, could be contrasted with that of white; other ideas seem to share a common source, such as light and fire, which quite often go together. These ways of building up information, Locke thought, are the main means by which we turn simple ideas into complex ones.

But how certain is such knowledge? Locke considered that there are 3 main types of knowledge:

1. Intuitive. This form of knowledge is the most certain because it seems the most obvious to us and the most difficult to doubt. This would be such things as "I have a body", "Black is not white", but also - according to Locke - "God exists". These are so obvious that we accept them intuitively.
    
2. Demonstrative. When we begin to put simple ideas together to form complex ones, we are demonstrating something. So, for example, if I compare the heat of the Sun with the heat of a fire, I may demonstrate that they are both made of similar substances.
   
   
3. Sensitive. This form of knowledge is the most uncertain because it relies merely on the evidence of the senses. If I look to see how many chairs there are in another room, I am relying on sensitive knowledge, which - as Descartes has shown - can, in some cases, be mistaken.

Discussion

Locke's idea of intuitive knowledge seems very similar to Descartes' concept of clear and distinct ideas. Is Locke any more successful in presenting an account of how we may be certain?