and a principal founder of phenomenology. Trained at Leipzig and Berlin, Husserl discovered philosophy by attending lectures of Brentano in Vienna. He subsequently taught at Halle, Göttingen, and Freiburg. From Brentano he inherited the view that the central problem in understanding thought is that of explaining the way in which an intentional direction, or content, can belong to the mental phenomenon that exhibits it. Mental phenomena are founded in sensory data, but whereas for Brentano there is no sharp distinction between ‘intuitions’ (Anschauungen) and concepts (Begriffe), Husserl reinstates the Kantian division. The distinctive feature of this way of thinking is that the content is immanent, existing within the mental act, and anything external drops out as secondary or irrelevant to the intrinsic nature of the mental state. In his earliest work, On the Concept of Number (1887, recast as the Philosophie der Arithmetik, 1891), Husserl applies Brentano’s psychology to the problem of our knowledge of arithmetic, attempting to find an acceptable empiricist account of the process of abstraction whereby we apprehend the numerical properties of aggregates. Frege believed that the mingling of subjective and objective elements in this work of Husserl produced an ‘impenetrable fog’, but he may have been insufficiently sympathetic to the dominant psychological aim of Husserl’s work. The problem of reconciling the subjective or psychological nature of mental life with its objective and logical content preoccupied Husserl from this time onwards. The next fruit of his attack on the problem was the elephantine Logische Untersuchungen (3 vols., 1900–13, trs. as Logical Investigations, 1970). Husserl eventually abandoned his attempt to keep both a subjective and a naturalistic approach to knowledge together, abandoning the naturalism in favour of a kind of transcendental idealism. The precise nature of this change is disguised by his penchant for new and impenetrable terminology (see noema), but the ‘bracketing’ of external questions for which he is well-known implies a solipsistic, disembodied Cartesian ego as its starting-point, with it thought of as inessential that the thinking subject is either embodied or surrounded by others. However, by the time of Cartesian Meditations (trs. 1960, first published in French as Méditations cartésiennes, 1931), a shift in priorities has begun, with the embodied individual, surrounded by others, rather than the disembodied Cartesian ego now returned to a fundamental position. The extent to which this desirable shift undermines the programme of phenomenology that is closely identified with Husserl’s earlier approach remains unclear, but later phenomenologists such as Merleau-Ponty have worked fruitfully from the later standpoint.