Linguistic Library (Mike Green)

Combined with its subject , the verb becomes the central element of a sentence or clause.  A main verb is the head word of a verb phrase - sometimes called a verb chain , e.g. 'He hit him hard.'  A lexical verb is the part of the verb chain that suggests the action involved, e.g. He might have hit him. A verb that tells of a 'state of being' is a copular or stative verb, e.g. is, was, seems, appears, becomes, etc. Verbs that work along with a subject are called finite (e.g. the girl looked). But verbs do not have to work with a subject within a sentence - these are called a verb's non-finite forms (e.g. I like to run). Non-finite forms of verbs can act as other parts of speech:     

• 'Only the cooked apples should be used.'
  

A verb phrase has a head word that is a main verb along with one or more 'helper' or auxiliary verbs.

A verb phrase is a coherent group of words that acts as a unit of meaning and which most often follows a subject (which is usually a noun phrase). Along with its subject the combination forms a clause. Both single verbs and verb chains tell what the action or state of their subject.

In a verb phrase, the main verb can be inflected to show tense (e.g. eat, eaten, ate), agreement (e.g. I eat, she eats) or continuous action (e.g. He is eating) and it can also be pre-modified with an adverb (e.g. He is quietly eating) the auxiliary verb can be inverted to form a question (e.g. Do you eat spaghetti?), e.g. 'She will have been singing for forty minutes.'

The voice of a verb can be either active or passive. The active voice is the most common and preferred in English usage. In an active clause the subject and object of the main verb are in their usual position, i.e. SVO, 'Alex caught the thief' however, in a passive sentence, the object is transferred to the subject position, e.g. 'The thief was caught by Alex.' This can have the effect of emphasising the object or diminishing the effect of the subject. in fact, in a passive construction, the subject can be hidden completely, e.g. 'The thief was caught.'

In the active voice, 'The cat sat on the mat' becomes, in the passive voice, 'The mat was sat on by the cat'. The passive voice is used when the style demands that the object of the action is to be given emphasis over the subject by what is called fronting of the object. What makes the passive useful is that it gives the possibility of reducing or removing the reference to the subject to diminish the role of the subject in the action of the sentence. This style popular in newspaper headlines which want to sound authoritative and impressive yet not point the finger to the cause of an action, e.g. 'Woman murdered in gangland shooting'. Here the subject (called the agent, or the agency of the verb) is not even mentioned and allows a very different style of sentence to be created. The passive voice is also the style of choice for reports where the subject is not important, e.g. the person who carried out an experiment or interview is usually of far less importance than the details and results of the experiment.