 In the context of this exchange, in the same letter of 13 September 1645, Elisabeth asks Descartes to “define the passions, in order to know them better” (AT 4: 289). It is this request that leads Descartes to draft a treatise on the passions, on which Elisabeth comments in her letter of 25 April 1646, and which is ultimately published in 1649 as The Passions of the Soul. Elisabeth’s concerns about our ability to properly evaluate our actions lead her to express a further concern, this time about the possibility of measuring value objectively, given that we each have personal biases, whether by temperament or by matters of self-interest. Without a proper measure of value, she implies, Descartes’s account of virtue cannot even get off the ground, for it is not clear what should constitute our best judgement of what is the best course of action. Behind Elisabeth’s objection here is a view of ethics akin to that of Hobbes and other contractarians,  which takes the good to be a matter of balancing of competing self-interests.