Why Hume's motivational argument cannot help non-cognitivism

In the modern metaethical debate, the term 'non-cognitivism' is often used to describe a claim in moral psychology: the claim that moral judgments are constituted by desire-like mental states rather than beliefs. An argument traditionally employed in defences of non-cognitivism is the 'motivation argument' which can be traced back to David Hume. The motivation argument combines the idea that moral judgments are motivationally efficacious states of mind with the idea that beliefs are incapable of exerting motivational force. The aim of this paper is to take a closer look at the second premise of the argument, often referred to as the orthodox Humean theory of motivation. I want to demonstrate that the orthodox Humean theory asks for a specific kind of contextualization and is most plausible if embedded into a variant of psychological hedonism. However, once the second premise is understood in this manner, the motivation argument can no longer give non-cognitivists what they are after.