Sub-classification of the Semi-auxiliaries
The definition of semi-auxiliaries is that a multi-word construction based on an auxiliary verb and having some of the same grammatical characteristics,also known as a semi-modal or a lexical auxiliary. As we can say, among the auxiliary verbs, we distinguish a large number of multi-word verbs, which are called semi-auxiliaries. These are two-or three-word combinations.
Semi-auxiliaries constitute a category of verbs between auxiliaries proper and main verbs. Some are followed by an infinitive; others by a zero infinitive.Structurally , semi-auxiliaries fall into three types:one type is initiated with the verb be :
|be able to |be about to |be apt to |be bound to |
|be due to |be going to |be likely to |be liable to |
|be meant to |be supposed to |be willing to |be obliged to |
A second type is initiated with the verb have ( have to) : Have to is the only semi-auxiliary beginning with have rather than be , but its inclusion in this category is partly justified by its occurrence in the full range of nonfinite forms , a respect in which it differs from the semantically parallel have got to; the third type is initiated with the verb seem, chance , happen , appear , etc. Syntactically,semi-auxiliaries can be divided into two subclasses depending on whether they can be transformed into an "it...that-clause" construction:
1.Those that cannot transformed into"it .. that + clause" is SubclassⅠ(be sure to,had better/best,have to,tend to,be certain to,turn out to)
2.Those that can be so transformed is SubclassⅡ(seem to,happen to,appear to,be certain to,be likely to,chance to,turn out to)
Like other auxiliaries, the semi-auxiliaries occur before main verbs.For example:I'm going...