‘Scientific questions may interest me, but they never really grip me’

In the opening decades of the twentieth century, many philosophers came to believe there are just two types of investigation, investigation that seeks to determine how the world is constituted and behaves and investigation that proceeds wholly independent of how the world is. They argued that when it comes to the question of truth, there is no such thing as knowledge that is at once factual and necessary, that is –as the jargon has it –synthetic a priori. In their view, science and common sense fall on one side of the fence, logic and mathematics on the other side, and nothing falls in-between. Philosophers of this stripe deemed metaphysics futile and unneeded and took philosophers of the past to task for assuming it possible to go one better than scientists and logicians and reveal how things are fundamentally. Such thinking, they maintained, is outmoded, even meaningless, to be avoided at all costs. Like David Hume (1711–1776), who held that genuine inquiry concerns matters of fact or relations of ideas, they dismissed swathes of philosophy as sophistry and illusion. They only differed in the firmness of their denial of a middle ground and how deeply it shaped their philosophy.

Wittgenstein was as uncompromising as anyone in his rejection of the possibility of a third kind of inquiry. In fact, he was a leading foe. Practically from first to last, he deprecated metaphysical speculation and repudiated the possibility of knowledge that straddles the fence, that claims to be as necessary as logical knowledge and as factual as scientific knowledge. While he initially affirmed that ‘philosophy consists of logic and metaphysics: logic is its basis’ (Notebooks, p. 106; dated October 1913), he almost immediately declared metaphysics out of bounds. In the Tractatus, compiled a few years later, he proclaims that propositions are ‘picture[s] of reality’, none of which are ‘a priori true’, and ‘outside logic all is accident’, there being ‘only logical necessity’ (Tractatus 4.021, 2.225, 6.3 and 6.37). More emphatically still, a decade or so later, he is reported as saying he would counter those who take there to be ‘a third possibility’ by noting that ‘it is indeed possible to make up words but I cannot associate a thought with them’ (Waismann, Wittgenstein and the Vienna Circle, p. 68).