My formulation of the distinction drawn by Wallerstein between defence mechanisms and defence contents (or other defensive behaviours) emphasizes two differences: (a) Defence mechanisms have an innate basis and originate with the differentiation of the rest of the ego, whereas defence contents are compromise formations produced by a complex process in which the defence mechanisms play an important part. (b) Defence mechanisms and their activity are unable to become conscious under any conditions, whereas defence contents, if not repressed, are capable of becoming conscious. I clarify this distinction by using the concept of a causal chain in which the defence content is the proximal cause of the defence effect, defined by Brenner as the minimization of unpleasurable affect, and the operation of the defence mechanism is a more distal cause through its role in causing the defence content. I compare my views with those of Brenner, Schafer, and Wallerstein regarding this distinction.