Are modal verbs finite or non-finite?
According to Oxford Dictionaries Online,
finite ... 2 Grammar (of a verb form) having a specific tense, number, and person.
non-finite ... Grammar (of a verb form) not limited by tense, person, or number.
Modal verbs (can, may, should etc) are always followed by bare infinitives. For example:
We could practice our dialogue.
Here, practice is a bare infinitive and is a non-finite verb and can, by its own nature, does not express tense, person or number.
Does that imply that in sentences like the one above, where a bare infinitive follows a modal verb, neither is a finite verb? If so, am I correct in understanding that we can have grammatically legitimate clauses and sentences even without a finite verb?
Solution 1:
I think you are misunderstanding the meaning of finite. Finite is not a category of verb but a category of verb forms and uses.
Finite forms are those which must take either past or non-past tense (must is anomalous in having the same form for both tenses) and may change to agree with the person and number of their subjects. Non-finite forms, infinitives and participles, do not change with tense of the utterance or person or number of the subject.
In your example, the modal verb could is finite: it is the "past" form of the verb can. (It may not express past tense, but that is another matter.) As you say, it doesn't take a particular inflection which expresses person and number; but no English verb has a complete repertory of such inflections. You will find a little more information at this question.
In fact, the full modals can, may, must, shall, will differ from other verbs in being defective: they have only finite forms, no infinitive or participles.
Every complete clause has exactly one finite verb✲; if there are more verbs strung together, then the first is finite and the rest are non-finite. Consequently, if there is a full modal verb it must be the first in the string.
✲ Except in cases where two or more finite verbs are conjoined: I can and will do it. But these cases really express two or more clauses.
Solution 2:
The definitions in Oxford Dictionaries Online describe some common traits of finite and non-finite verbs in English, but they overlook the key differences that you'd use to analyze an actual sentence. Wikipedia offers a more thorough explanation:
A finite verb is a form of a verb that has a subject (expressed or implied) and can function as the root of an independent clause.... In many languages, finite verbs are the locus of grammatical information of gender, person, number, tense, aspect, mood, and/or voice. Finite verbs are distinguished from non-finite verbs, such as infinitives, participles, etc., which generally mark these grammatical categories to a lesser degree or not at all....
English is one of the many languages that only inflects finite verbs. However, inflection is not a defining trait, because some verb classes lack inflection for other reasons. The preterite-present verbs are one such class that inflects only for tense.
That class includes the English modal verbs, which have two relevant properties:
- They do not inflect, except insofar as some of them come in present–past (present–preterite) pairs. They do not add the ending -(e)s in the third-person singular....
- They are defective: they are not used as infinitives or participles..., nor as imperatives, nor ... as subjunctives.
Thus:
- Some modals do inflect for tense.
- Those that don't inflect do so for linguistic reasons, not grammatical reasons.
- Modal verbs are only used as finite verbs, as the root of the sentence.
Therefore, in the sentence “We could practice our dialogue,” could is a finite verb, functioning as the root of the sentence, that modifies the non-finite verb practice.