There are several words that can be used as synonyms for the word "rationalistically". Some of the words that come to mind include "logically", "reasonably", "analytically", "intellectually", "scientifically", and "thoughtfully". Each of these words expresses the same idea of approaching something in a logical and calculated way, rather than relying on pure emotion or intuition. Whether you are writing an academic paper, defending a argument, or simply trying to make a decision, these synonyms can help you convey the sense of rationality and careful reasoning that is essential to making good choices and understanding the world around us.