Note that I am using rationalist in its strict philosophical sense, as in rationalist like Descartes or Leibniz, not rationalist as it might be understood colloquially. from the Encyclopedia Britannica:
Rationalism, in Western philosophy, the view that regards reason as the chief source and test of knowledge. Holding that reality itself has an inherently logical structure, the rationalist asserts that a class of truths exists that the intellect can grasp directly. [....] Rationalism has long been the rival of empiricism, the doctrine that all knowledge comes from, and must be tested by, sense experience. As against this doctrine, rationalism holds reason to be a faculty that can lay hold of truths beyond the reach of sense perception, both in certainty and generality.
In this question, the OP wonders whether materialism and empiricism are the same or not. It is pointed out in the answers that empiricism and materialism are not the same at all, one being an epistemic method, while the other is an ontological position, and that they shouldn't be conflated.
Although I understand that the two are not the same, I feel that the OP is right in sensing a relation between the two, for the following reasons:
- Although not all empiricists are materialists, those that are materialist are so based on an empiricist position of believing only in that which can be observed.
- Insofar as empiricism's antithesis is rationalism (See the SEP article), one can say that while empiricism doesn't necessarily imply materialism, its antithesis, rationalism, does imply some form of idealism or at least dualism, for how else would there be truths that are directly knowable by the mind, regardless of the senses?
- Is it possible to be both a rationalist and a materialist? How can one reconcile materialism with the idea (see what I did there :-)) that there are truths which are independent of sense data?
- Have there been any famous rationalist materialists?