However, when he applies the term to the world of living things, he uses it in several distinct, but related, senses. The first biological sense in which Aristotle uses eidos is close to the English meaning of ‘form’ – as the appearance of an animal. His word for a taxon of animals is genos (pl. genē) – which I translate as ‘kind’. Some genē are small – the sparrow kind; others are large – the bird kind. So when he wants to describe the features that make a sparrow a sparrow rather than a crane, or a bird a bird rather than a fish, he speaks of its eidos.
