One of Husserl's leading ideas in the field of practical and evaluative Reason is the idea of an analogy between ethics and logic. This method is required in order to constitute ethics as a pure science. But how has this analogy to be understood and justified? Does it mean the control of theoretical reason on the acts of willing and feeling? Is it to say that ethics and logic are similar, or are sharing some essential features? In what sense may we assert that an analogy is not a pure identity? This paper tries to provide some answers to those questions, through an examination of the meaning and the function of this central concept of analogy, which is firstly introduced in Husserl's writings on mathematics (Philosophie der Arithmetik) and logic (Logische Untersuchungen).