AVESTAn scholars have long believed that the duality which is the corner-stone of Zoroastrianism in the Avestā, finds its counterpart in the AVESTAn language; there are a certain number of words in AVESTAn which are used only for Ahurian creatures, and likewise there are a number of other words which are reserved for Ahrimanian beings. The author sets out in this paper to verity this assumption, and also to find out the origin of such a linguistic dichotomy.After reviewing and rejecting the opinions of some European scholars on the subject, for instance the claim that the words associated with Ahriman were originally those that were used for beasts or for one's enemies, the author lists some of these words which have "Ahurian" and "Ahrimanian" varieties; he gives a list for nouns (which includes some very common words such as house, woman, death and parts of the human anatomy) and another one for verbs (such as to create, to come, to eat, to go etc).The author then subjects these words to a linguistic and etymological analysis and comes up with some interesting findings:1. Some words are used metaphorically, either for Ahurian or for Ahrimanian beings. In some cases, we find the words which are associated with Ahura Mazda are euphemisms for some more common words.2. In some cases, the words which are used for Ahrimanian beings are diminutive and pejorative.3. Likewise, some words used for Ahrimanian beings have been picked from a local dialect, which was considered inferior to the main AVESTAn dialect.The author concludes that this duality is not in fact linguistic; it is rather stylistic, and it is a deliberate effort by those high priests who were responsible for composing AVESTAn texts to show on the one hand their veneration for Ahura Mazda and his creations, and their disdain, on the other, for Ahriman and his cohorts.