John Locke provides his definition of knowledge in An Essay Concerning Human Understanding, written in the late seventeenth century.  Locke believed knowledge is obtained the moment you perceive that you agree or disagree with an idea.  He described three types of knowledge.  Intuitive knowledge is not based on any immediate facts but is instead something we just know to be true.  For example, you may know that someone loves you.  You may have a direct and immediate recognition of this knowledge even though you may not be able to trace the knowledge back to one specific event.  

Demonstrative knowledge is defined by Locke as knowledge obtained through a series of thoughts or chain of reasoning.  For example, you may know that Jimmy likes everything that Sally likes.  If you also know that Sally likes dogs, you can conclude through demonstrative knowledge that Jimmy will also like dogs. 

Locke’s third type of knowledge is defined as sensitive knowledge.  This is when you become aware of knowledge from a sensation outside of yourself.  We may know that someone is entering a room because we smell their perfume.  We may not even recognize the role of smell in our thought process, but our senses give us additional knowledge.  There has been much debate over sensitive knowledge and whether it truly exists or if it is just another form of intuitive and demonstrative knowledge.