Metaphor was based on similarity. During their history the Arabs adopted different logical systems in their scientific investigations. They shifted from Aristotle's logic accepted by the philosophers to that of the theologians and jurisconsults, and later again back to Aristotle's logic. In all these logical systems the definition of metaphor was dependent on the ever changing meaning of “similarity”. The seemingly unchanging definition of metaphor implies different interpretations in different ages parallel to the changing logical background.