Propositional attitude verbs seem to be examples of what we can call opacity verbs. That is, they seem to create linguistic environments that do not permit substitution of co-designating singular terms salva veritate. This is the basis of Frege's puzzle. Modals like it is necessary that and it is possible that are also opacity inducing. Opacity verbs give rise to a de re/de dicto distinction. The de re/de dicto distinction has meant different things to different people. Below we'll distinguish three different conceptions of this distinction, the first two concerning the status of sentences and the third being more metaphysical. But first let us motivate the distinction.