Variation is the procedure used by both Bolzano and Frege to define their respective notions of the objective content – or, rather, the direct object – of thought (representations in themselves and sense, respectively) They use it in utterly different ways, though: for Bolzano resistance to variation is essential to all representations in themselves, simply as such, while for Frege it is the hallmark of (both the reference and) the sense of unsaturated expressions only, the saturated ones being rather extraneous than resistant to variation. However, the two notions thus defined are not barely incommensurable: there is a matter between them. Moreover, in each of the two philosophers variation – and therefore thought – implies drawing a profile of the entire world: by predicating or simply by representing, thinking implies outlining nothing less than the world. From both Frege and Bolzano variation can be traced forward to XX century transcendental philosophy: Wittgenstein, Husserl and Heidegger all share this background.
