Geach insists, in opposition to the behaviourism of the day, that there are episodic mental acts such as acts of judgment. How to characterize such mental acts remains as problematic as it was fifty years ago, and his book still has much to teach us. He begins with an attack on the abstractionist theory of concept-formation, then goes on to critize the relational theory of judgement propounded by Bertrand Russell. Moving from criticism to construction, Geach first offers an improved version of Russell's analysis, them moves on to offer an alternative of his own.