In the work of Hermann the Dalmatian De essentiis, the only Hermann’s original work, the presence of different philosophical schools is recognizable. Even a superficial analysis of the work De essentiis shows however that it was Plato’s dialogue Timaeus which played the decisive role in shaping Hermann’s philosophy, or, to put it more precisely, it was Calcidius’s translation of Timaeus and his commentary of the same work written toward the end of the 4th century. Calcidius’s translation of Plato’s most famous dialogue was in fact the only source of knowledge of Plato’s philosophy in the West until the 12th century. Particularly important role the translation and the commentary of Calcidius played in the 12th century at the school of Chartres, with which Hermann was closely related, where, even before the awakening of the interest in Aristotle’s natural philosophy, an intensified interest in the study of nature, independently of Church teachings took place primarely thanks to the renewed interest for Plato’s Timaeus. From the very beginning of the reception of Plato’s Timaeus in the West one of the key issues in the interpretation of this dialogue was the question of matter. It is especially to that issue that Calcidius dedicated the most extensive part of his commentary of Timaeus. This is also one of the fundamental issues of Hermann’s philosophy. Until now there was no detailed study on the role Calcidius’s translation and commentary of Timaeus played in the formation of Hermann’s philosophy nor was there a comparative analysis of Calcidius’s commentary of Timaeus and Hermann’s work De essentiis. Therefore in the present paper we explore primarily the possible impact Calcidius had on the formation of Hermann’s attitudes related to the one of the most important issues in the philosophy of the 12th century, that is, to the question of matter.