This paper is composed of three parts, starting with a brief description of the textual basis of Sâmkhya-Yoga. The second part is concerned with the concept of three kinds of valid knowledge; it discusses the relationship between the definitions of valid knowledge in the pramâna-section of the Pâtañjala-yoga-sâstra (PYS) 1.7 and notions of valid knowledge apparent in various other passages of the text. This relation is shown to be a complicated one., since the views on valid knowledge applied in the body of the text more than once differ considerably from those which one would expect against the backdrop of the pramâna section. This result leads to the conclusion that the theories of valid knowledge as expounded in the pramâna section are probably innovations to the classical Sâmkhya-Yoga. The third and final part of this paper deals with the role of the pramâna-section in the PYS. I argue that this passage does not, in the first place, aim at a philosophical clarification. Patañjali upholds his special pramâna-theories in order to create acceptance for—or belief in—the soteriological efficiency of Sâmkhya-Yoga.