Mair's (1990) very thorough and encompassing study of Infinitival Complement Clauses in English, which includes a section on "The textual and structural factors responsible for the skewed relationship between actives and passives," is based on evidence from the corpus of the Survey of English Usage, which at the time Mair collected his data comprised 895,000 words (Mair 1990: 13), but "[t]he only passive matrix verb attested often enough in the corpus to warrant any definite conclusions is say" (Mair 1990: 183), of which there were 24 occurrences.
The predominance of passive matrix verbs with infinitival copular complements
Restricting ourselves to the 23 verbs for which the total number of attested infinitival complements exceeds one hundred (Table 2), there are even five verbs that more often have an active than a passive matrix. If there is a general principle that accounts for the high occurrence of passives, these deviations from this principle will need to be explained as well.
Mair (1990: 178) has already dismissed the explanation offered by Bolinger (1977: 129) that "[t]hese verbs express opinions and viewpoints concerning which the speaker, when he wants to sound impressive, would rather shift responsibility to some unnamed--and hence remote and powerful agent," which passive matrix verbs allow them to do, saying that "to trace back the emergence and spread of a grammatical construction solely to the speaker's psychological stance does seem far-fetched." Without question the popularity of many of the (BE) Ved to be patterns, particularly in genres like news texts and scientific discourse, can be related to the fact that these patterns have become grammaticalized as lexicogrammatical paradigmatic options available in systems of "evidentiality" (cf.