In the first book of his Physics, Aristotle investigates the principles and causes of natural things, and discusses the relevant theories of his predecessors. Having rejected the doctrine of the Eleatics (Phys. A 2–3), he turns in Phys. A 4 to the natural philosophers and argues against the infinity of Anaxagoras’ principles. This paper presents the interpretation of the Aristotelian discussion in Phys. A 4 given by Themistius (fourth century AD) in his commentary on Aristotle’s Physics (In Phys., CAG, ed. H. Schenkl, V 2, pp. 13, 9 – 17, 26). The text of Themistius is divided into sections corresponding to the arguments of Aristotle, translated into Polish, preceded by an introduction and provided with explanatory notes.