It is almost universally accepted that semantic properties—such as meaning and content—supervene on some class of non-semantic properties. This is roughly to say that any two possible worlds that are alike in non-semantic respects are alike in semantic respects. More precisely,


Semantic Supervenience. For any two metaphysically possible worlds, w and w¢, and for any two individuals, x in w and y in w¢, any isomorphism between x and y that preserves non-semantic properties preserves semantic properties.


In this paper, I take issue with Semantic Supervenience. I start by assuming haecceitism, the view that in addition to qualitative properties, such as having a certain mass or height, there are haecceitistic properties, such as the property of being identical to Socrates. I argue that, assuming haecceitism, friends of Semantic Supervenience face a dilemma. On the first horn of the dilemma, if the non-semantic properties that figure in the supervenience base are assumed to be purely qualitative properties, Semantic Supervenience is false (Magidor and Kearns 2012). On the second horn of the dilemma, if the non-semantic properties in the supervenience base are assumed to include all non-semantic haecceitistic properties, this trivializes Semantic Supervenience. The remainder of the paper considers and rejects responses to this dilemma, such as denying haeccitism or including some but not all haecceitistic properties in the supervenience base.