Rationalism is an ism which, in a nutshell, says that it can be possible to determine the truth of a statement (= logi) by thought alone.

Rationalism and empiricism (which uses experience) are often contrasted. For hundreds of years, science has relied only on empiricism to determine the truth of theories. Theories which could not be proved empirically, only rationally, are not considered fact. An example of a theory which can not be justified empirically, only rationally, is String Theory.

There are problems with relying only on empiricism:

• Experience can change depending on the observer
• Experience may not accurately reflect truth