  Frege conceived of thoughts as structured complexes of senses. The thought expressed by ‘The evening star is bright’ consists of the sense of ‘the evening star’ and the sense of ‘is bright’. (It should be noted that this claim about structure does not strictly follow from the fact that sense is compositional, i.e., that the sense of a whole expression is fixed by the senses of its constituent parts and their syntactic mode of arrangement.) In his late masterpiece, “The Thought” (1922), Frege is explicit about the nature of thoughts. They are not part of the outer realm, which consists of those entities perceivable by the senses. This Frege thinks is obvious. Nor are they part of the inner realm, which consists of ideas. Unlike ideas, thoughts do not require an owner (i.e., they exist even if not present in any mind), and can be present to more than one mind. A third realm must be recognized, he tells us — a realm of abstract eternal entities which we can grasp by virtue of our power of thinking. However, Frege is explicit that thoughts do act: