Peter Geach, who has died aged 97, was a formidable logician and happened to be married to one of the 20th century’s leading English-language philosophers, Elizabeth Anscombe.
In a way this meant he was overshadowed. He did, though, have a strong philosophical life of his own, and without the thousands of hours of discussion that Elizabeth Anscombe had with him, her philosophy would not have attained the eminence it did.--The Telegraph
The quoted passage above are the first lines of an unsigned obituary of Peter Geach. It makes a remarkable claim: that his presence was decisive in her achievements. It's possible to read it as a sociological point: Geach was needed for Anscombe's status in the profession. But the more likely intended reading is that talking to him made her a much better philosopher. It's offered without evidence. Even if Anscombe says something as much somewhere, the counterfactual is hard to evaluate.* In addition, the obituary also offers an unflattering comparison between Geach and Anscombe: "Unlike the dense, unsignposted [sic] prose of Anscombe, Geach’s style was a pleasure to read." It does not occur to the author that, perhaps, on the whole, Anscombe was struggling to make genuinely original points on unwieldy topics, while Geach was working with a lot more self-imposed constraints.
In a curious lack of symmetry, the obituary does not assign Anscombe any responsibility for Geach's eminence or achievements. I am not an expert on the thought of either, but if one claims that Geach is a "honorary founder of the philosophical school that called itself “analytical Thomism,”" why not mention Anscombe at all? So, it's quite possible, of course, that Geach improved her philosophy, but we can't rule out the possibility that either his ideas sometimes made hers worse or that his presence was a net-zero in her philosopher career (etc.) Perhaps, one day there will be careful dispassionate scholarship on the issue.
*I think it is almost certainly less true than the comparative claim that without Wittgenstein, Anscombe's philosophy might have been very different.