Every syntactical well-formed statement must contain just one finite verb. Finite verb forms are tied to the grammatical subject and the morphology is inflected to indicate person, number, tense, aspect, voice and mood.
It is possible to have more than one verb serving as the finite verb is such constructions as they come and go or you can walk but not run. These are really cases of elision, a short form of they come and they go and they can walk but they cannot run.
Similarly, although there is multiple verb form used in such statements as we must try and go, this is an idiomatic replacement for we must try to go rather than a syntactically correct form.
Person, number & tense
To reflect person, number and tense most verbs in English have 3 finite forms. A small number have only 2 and the copula to be has 6 forms.
Mood
There are 7 grammatically distinct moods in English: indicative, subjunctive, imperative, optative, hortative, conditional and interrogative. The most common mood is the indicative, which is the descriptive, evocative and declarative mood.
The subjunctive mood on the other hand is used to convey some level of unreality. The subjunctive in English is falling out of use. One reason may be that in most circumstances it is indistinguishable from the indicative. It is only in the way the verb to be is inflected and in the 3rd person singular of other verbs that any distinction is observed. The only form that still idiomatic is the past tense of the verb to be where we are still likely to say if it were rather than if it was. However, in idiomatic usage we would typically say I hope that it is the case rather than I hope that it be the case and though he has to go rather than though he have to go.
The imperative, hortative and optative all share the same form and can be difficult to distinguish. The imperative is the form for commands and requests, the optative is used to express wishes and the hortative to offer exhortations. These forms are the same as the subjunctive except that they are only used in the present tense and, unlike the subjunctive, they are not becoming obsolete. Syntactically, statements in these moods are the only kind that do not require a grammatical subject.
Logically, as these moods target an event that is happening is about to happen, they cannot have a past tense or a perfect aspect. However, they can have a continuous aspect: for example, be going now!
The conditional and interrogative moods are morphologically the same as the indicative mood. Conditionality is usually conveyed through using the conditional forms of the modal auxiliaries or by using a hypothetical construction such as if…then.
Similarly, there are a number of ways of asking questions. The word order can be reversed in a question or an interrogative pronoun can be used. In the spoken language the words can be spoken with a rising intonation. In the written form, the question mark can be used.
Aspect and voice
There are 13 auxiliary verbs in English. The most commonly used auxiliary verbs are to be and to have which are used to indicate aspect and voice. There are also the verbs to do, which can be used as an auxiliary in questions and to add emphasis and to let, the permissive auxiliary used to indicate that the event was allowed to happen by the agent rather than being a positive action. There are also nine modal auxiliary verbs: can, could, will, would, shall, should, may, might & must. These are dealt with in the next section.
As an auxiliary the verb to be is used to convey the passive voice and continuous aspect and similarly the verb to have is used to convey the perfect aspect. Both together are required to indicate the continuous perfect aspect.
As the table indicates, the continuous perfect isn’t possible in the passive voice. The logical forms are *have been being spoken in the present and *had been being spoken in the past. The problem is that something cannot both have been and still be being as these are two incompatible states. Instead, we will normally use the continuous aspect.
As well as to be and to have, the verb to do can function as an auxiliary to convey emphasis or to pose questions while the verb to let is used as an auxiliary to indicate where something is allowed to happen or should be allowed to happen.
Modal auxiliary verbs
There are 9 modal auxiliaries, of which 4 are alternative forms which can be used to indicate either the past tense or conditionality. The modal auxiliaries will and would used to be equivalent to the construction to want to but this meaning is largely obsolete and they are now used to form the future tense and the conditional mood. The use of could and might in the past tense is becoming unidiomatic.
In the perfect aspect there are a number of additional nuances. Modal auxiliaries are used to express ideas about conditionality, possibility and necessity and when the event is still in progress these imply open outcomes. However, when an event is completed the outcome is no longer open, so, in this case, the implication of conditionality and possibility shifts to our knowledge of the event rather than the event itself.
The next table explains the meaning when the event is completed in the future. The event is in the future, but viewed from a point in time when the action is completed
The next table shows the meaning when the event has been completed but we haven’t yet received the information. The event is viewed as having been completed but the outcome is not known.
The perfect used with conditional version of each modal auxiliary indicates that the conditional state or event was not realised. The event is complete now but the conditionality and possibility were a part of the way the event evolved.
Modal auxiliaries can also be used with an infinitive in the continuous and perfect continuous but, as in other cases, the perfect continuous is not possible in the passive voice.
Phrasal verbs
One feature of English is the prevalence of phrasal verbs, something that non-native speakers find difficult in what is otherwise, at the basic level, quite a simple language. Phrasal verbs are formed by the addition of additional particles, typically prepositions or adverbs, to form a verb.
There is a potential for ambiguity when a phrasal verb constructed with a preposition is followed by a prepositional phrase. In the following example, is about the results a prepositional phrase in an adverbial qualifying the intransitive verb to think or are the results the direct object of the phrasal verb to think about. The ambiguity can be resolved by testing to see whether or not the passive is possible. If it is, the statement is transitive.
“To” as particle and preposition
Although many prepositions can function as particles when added to phrasal verbs, the word to in particular has multiple functions. As well as being a preposition in a prepositional phrase and before an indirect object, where it represents the dative case, it can also function as a particle attached to a phrasal verb and a particle attached to an infinitive.
