De dicto and de re
The terms de re (Latin: "about the thing") and de dicto (Latin: "about what is said") refer to two distinct interpretations of Noun Phrases that emerge in intensional environments involving a participant's knowledge or belief states about a proposition (also known as propositional attitude reports). A classic example from Quine (1956) is (i), which displays the two readings.
(i) Ralph believes that someone is a spy. de re reading: Ralph believes of somebody x that x is a spy. de dicto reading: Ralph believes that there is a spy, though he doesn't know who in particular it is.
The de re reading of (i) states that Ralph has a belief about a particular person being a spy. For example if Ralph observes his coworker Hubert making photocopies of top-secret documents, (i) would be appropriately used because Ralph believes that someone (namely Hubert) is a spy. The de dicto reading is a statement about the subject's beliefs about the more general existence of a spy. For example, if Ralph has not directly observed behavior indicative of spying, but has suspicions that there is a spy in his midst (e.g. if the enemy intelligence agency is consistently receiving top-secret intelligence information), then (i) would describe Ralph's beliefs de dicto that somebody is a spy.
(ii) Estefan thinks a dog bit him. de re reading: Estefan believes he was bitten by Fido. de dicto reading: Estefan believes he was bitten by some dog (or other)
Scope Ambiguity Theory
Cresswell, Maxwell J. and Arnim von Stechow. 1982. "De re" belief generalized. Linguistics and Philosophy (5: 505-535)
Kaplan, David. 1969. "Quantifying in" Synthese (19: 178-214)
Lewis, David. 1979. "Attitudes de dicto and de se". The Philosophical Review (88: 513-543)
Quine, W. V. 1956. "Quantifiers and Propositional Attitudes", The Journal of Philosophy (53: 177-187)