A lot of experimental data show that, very quickly and even downright unconsciously, our visual system snips out the morphemes of words. For instance, if I were to flash the word "departure" on a computer screen, you would later say the word "depart" slightly faster when confronted with it. The presentation of "departure" seems to preactivate the morpheme [depart], thus facilitating its access.
Psychologists speak of a "priming" effect—the reading of a word primes the recognition of related words, much as one primes a pump.
Importantly, this priming effect does not depend solely on visual similarity: words that look quite different but share a morpheme, such as "can" and "could," can prime each other, whereas words that look alike but bear no intimate morphological relation, such as "aspire" and "aspirin," do not#533•