The gerund is a nominal formation of a verb, in effect a (theoretically) declined form of the infinitive (a form distinct from the gerundive, which word properly is foreign to English grammar). The function is more clear in a language like Latin. Consider the verb fello, infinitive fellare. The gerund has the nominative neuter form fellandum, "giving a blow-job", genitive fellandi, "of giving a blow-job", and ablative fellando, "by giving a blow-job". The gerund thus denotes an explicit case-function within the sentence's grammatical structure.
Note, then, that the appearance of the gerund in English, as in the translations, is identical with the active participle. The distinction is crucial. Consider the following:
- John soliciting a prostitute was sentenced to several months community service
- John's soliciting a prostitute resulted in a nasty case of the clap
- John soliciting a prostitute increases his chance of contracting infectious diseases.
The grammatical subject in 1) is the proper noun "John", in 2) the gerund "soliciting", to which "John" is attached as a possessive; both of these contain proper usage. The third is an example of a common misusage termed a Fusion Participle, in which sentence there is no proper grammatical subject, since the full construction relies on a fusion of sense in the combination of "John" and the participle "soliciting". Neither John nor soliciting can be the proper subject, since "soliciting" would require John to stand in an absolute function, and John alone would not complete the required meaning. Certainly such constructions are perfectly viable in both Attic Greek and German, but pervert any sense of style in English.
A far more insidious breach of style is the confusion between the gerund and the infinitive. Consider which of the following, conceivably taken from a single conversation, is correct:
- "I do not look forward to pay my pimp his cut" or "I do not look forward to paying my pimp his cut."
- "I aim to cheat him out of the money" or "I aim at cheating him out of the money"
- "He has the duty to cut up that bastard who would not pay" or "He has the duty of cutting up that bastard who would not pay"
The possible variations and situations are endless, and I will not try to compile a list of restraints and exceptions; a few general rules may be given. Very often, the incorrect choice is made by analogy to a proper construction. Since the phrases "able to get it up and "adequate to perform" are English constructions, many writers incorrectly assume phrases such as "equal to perform" are equally valid. Likewise, the incorrect usage may be a subset of particular idiom, commonly accepted through frequent use. Thus "This house is not sufficient in size to contain such a clientele" leads to "This house is not equal in size to contain such a clientele".
Another fine distinction is the implication of agency. The infinitive, while it may contain an implication of a general agent, is usually incapable of further specification, while the gerund freely admits a possessive dependent. Thus "to err is human" has a generalizing force, while "His erring in my favour is a sign of his complete incompetence" allows the limitation to a specific case.
Much of this is based on the loving work of H.W. Fowler, in his A Dictionary of Modern English Usage, (Oxford 1950).