In one of the classes, I'm talking about slingshot arguments, and I was thinking about a possibly clear way of laying out Frege's argument that (if sentences have denotations) propositions aren't in general denotations of sentences, showing why the conclusion technically speaking doesn't follow, and how once an extra assumption is added the argument flies. Here's the result. (If you know and understand Frege, this probably won't surprise you, but I'm only concerned with a way of presenting this to students here). Frege in On Sense and Nominatum argues: Thus far we have considered sense and nominatum only of such expressions, words, and signs which we called proper names. We are now going to inquire into the sense and the nominatum of a whole declarative sentence. [...] Is this thought to be regarded as the sense or the nominatum of the sentence? Let us for the moment assume that the sentence has a nominatum! If we then substitute a word in it by another wor...