Rationalism is an ism which essentially states that it can be possible to determine the truth of a statement (= logi) by thought alone.
Rationalism is often contrasted with empiricism, which relies on experience to determine truth. For hundreds of years, science has relied only on empiricism to determine the truth of theories. Theories which can not be proved empirically, only rationally, are not considered strong. 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