This paper deals with John Wyclif 's account of the fallacia accidentis. To a certain extent Wyclif 's explanations fit in with Aristotle's understanding of language. Aristotle recognises that we can talk about substances in many different ways; we can introduce them by using 'substantial' names, but also by using names derived from the substances' accidental features. The substances are the ultimate foundation of all these expressions. This idea in itself is not opposed to a conceptualist account of language. John Buridan uses Aristotle's principle of categorisation to show how language works, but for him the activity of categorising things is to be explained in terms of our mental activities only. Wyclif, on the other hand, reads much into the requirement that all our linguistic distinctions should have their basis in extramental reality: our conceptualisations not only pertain to individual substances, but also parallel their distinct ontic layers.