Fruitful interdisciplinary contact between specialists in theoretical morphology and in various branches of psycholinguistics (my examples will come from acquisition, processing, aphasia) is hampered by reciprocal illusions, some of them rarely criticised explicitly. Often ecological validity is dubious. Arbitrariness between linguistic form and meaning is taken as foundational in language studies and the question of how linguistic form links to meaning is central to language development, processing and evolution. But, languages also display iconicity in addition to arbitrariness. This is especially evident in sign languages. This, what if the study of language started from signed rather than spoken languages? In the talk I will explore this question.