In Chapter 12 we discussed the apparent failure of compositionality in the complement clauses of propositional attitude verbs (believe, expect, want, etc.). This apparent failure is observable in several ways. First, the principle of substitutivity does not seem to hold in these complement clauses: replacing one NP with another that has the same referent can change the truth value of the proposition expressed by the sentence as a whole. For example, even if sentences (1a–b) are assumed to be true, we cannot apply the principle of substitutivity to conclude that (1c) must be true as well.
(1) a. Charles Dickens was the author of Oliver Twist.
b. George Cruikshank claimed to be the author of Oliver Twist.1
c. George Cruikshank claimed to be Charles Dickens.
Second, as illustrated in Chapter 12, a sentence which contains a propositional attitude verb may have a truth value even if the complement clause contains a NP which lacks a denotation. A third special property of these complement clauses is that NPs occurring within them may exhibit the de re vs. de dicto ambiguity.
These three properties are characteristic of opaqe contexts, i.e., contexts in which the denotation of a complex expression cannot be composed or predicted just by looking at the denotations of its constituents; we must look at senses as well. In recent work these contexts are often referred to asintensional contexts, for reasons that will be explained in §15.2.
In this chapter we discuss several types of intensional contexts. §15.2 reviews our earlier discussion of propositional attitude verbs, and explains the term intension. §15.3 discusses certain types of adjectives whose composition with the noun they modify cannot be modeled as simple set intersection. These adjectives are often referred to as intensional adjectives. §15.4 briefly discusses some other intensional contexts involving tense, modality, counterfactuals, and “intensional verbs” such as want and seek. §15.5 provides some examples of languages in which the subjunctive mood is used as a grammatical marker of intensionality. §15.6 briefly discusses the lambda operator, which is used to define functions, and how it can be used to represent intensions as functions.
1 Actually, George Cruikshank only claimed that “the original ideas and characters… emanated from me.” (www.bl.uk/collection-items/ge...harles-Dickens )