Comparative illusion

In linguistics, a comparative illusion (CI) or Escher sentence is a comparative sentence which initially seems to be acceptable but upon closer reflection has no well-formed, sensical meaning. The typical example sentence used to typify this phenomenon is More people have been to Russia than I have. The effect has also been observed in other languages. Some studies have suggested that, at least in English, the effect is stronger for sentences whose predicate is repeatable. The effect has also been found to be stronger in some cases when there is a plural subject in the second clause.

Escher sentences are ungrammatical because a matrix clause subject like more people is making a comparison between two sets of individuals, but there is no such set of individuals in the second clause. For the sentence to be grammatical, the subject of the second clause must be a bare plural. Linguists have marked that it is "striking" that, despite the grammar of these sentences not possibly having a meaningful interpretation, people so often report that they sound acceptable, and that it is "remarkable" that people seldom notice any error.

Mario Montalbetti's 1984 Massachusetts Institute of Technology dissertation has been credited as being the first to note these sorts of sentences; in his prologue he gives acknowledgements to Hermann Schultze "for uttering the most amazing */? sentence I've ever heard: More people have been to Berlin than I have", although the dissertation itself does not discuss such sentences. Parallel examples with Russia instead of Berlin were briefly discussed in psycholinguistic work in the 1990s and 2000s by Thomas Bever and colleagues.