Degrees of Knowledge by Kenneth Shouler, Ph.D.
Locke classified knowledge into three degrees, or levels: intuitive, demonstrative, and sensitive. Intuitive knowledge is immediate and is the highest kind of knowledge. Demonstrative knowledge results from a chain of reasoning, as in logic or mathematical proofs. Sensitive knowledge concerns those things you know that originate from your senses.
Intuitive knowledge consists of the immediate awareness of agreement or disagreement between two ideas. For example, you have an immediate, indubitable knowledge that five is greater than three.
Locke is similar to Descartes in thinking that people have an immediate knowledge of their own existence. If you know that you doubt, then you know (as Descartes had asserted) that you must exist in order to doubt. You also know intuitively that a square is not a triangle, that powder blue is different from royal blue, and so forth.
Demonstrative knowledge consists of understanding (by means of reasoning) the logical relationships among ideas. If you know that all men are mortal, and Socrates is a man, then you know demonstrably that Socrates is mortal. This deductive conclusion comes from a chain of reasoning. Other examples are the deductive conclusions of geometry and calculus.
Sensitive knowledge begins with perceptions of particular objects. You accept these perceptions as real, but they represent probable facts and not certain truths about the external world. Cause-effect relationships fall into this category. For instance, if you notice repeatedly that a certain event precedes a given result — like a cue ball contacting an eight ball and sending it into the corner pocket — you conclude that there is probably a cause-effect relationship between them. So your knowledge of such cause-effect relations begins with sensations.
