Among Spinoza’s principal projects in the Ethics is his effort to “remove” certain metaethical prejudices from the minds of his readers, to “expose” them, as he has similar misconceptions about other matters, by submitting them to the “scrutiny of reason”. In this article, I consider the argumentative strategy Spinoza uses here – and its intellectual history – in depth. I argue that Spinoza’s method is best characterised as a genealogical analysis. As I recount, by Spinoza’s time of writing, these kinds (...) of arguments already had a long and illustrious history. However, I also argue that, in his adoption of such strategies, we have good reason to think Spinoza’s primary influence was Gersonides. Elucidating this aspect of Spinoza’s critique of his contemporaries’ axiologies brings a number of explicatory and historical boons. However, regrettably, it also comes at a cost, revealing a significant flaw in Spinoza’s reasoning. Towards the end of this article, I consider the nature of this flaw, whether Spinoza can avoid it and its ramifications for Spinoza’s wider philosophical project. (shrink)