In Linguistics, de dicto/de re ambiguity is a logical issue in semantics and pragmatics.

Take the statement, "Jan wants to invite a clown to the wedding."

Assuming no contrastive stress, this has two readings:

1) the de dicto ("of what is said") reading - Jan wants to invite someone on the basis of them being a clown. He doesn't really care who the clown is, he just wants a clown to be present.

2) the de re ("of the thing") reading - Jan wants to invite an individual, say, Bozo, who happens to be a clown, and not necessarily because he's a clown.

These different readings are also represented differently in logic using predicate calculus.
W(x,Φ) - x wants to Φ where Φ is a proposition.
I(x,y) - x invites y to the wedding.
C(x) - x is a clown
j = Jan
And I will use E as the existential quantifier and subscript to represent my restrictions (I use restricted quantification.)

de dicto reading: W(j, ExC(x) I(j,x))
In English, roughly: Want holds between Jan and an Existant x, Clown of x, such that Invite holds between Jan and x.

de re reading: ExC(x) W(j, I(j, x))
English: There Exists an x, Clown of x, such that Want holds between Jan and x.