An infinitive is a form of the verb not inflected for grammatical categories such as tense and person and used without an overt subject. In English, the infinitive usually consists of the word to, followed by the verb, for example, to speak. The Infinitival clause is a clause containing an infinitive as its main or only verb form. However, an infinitive clause can also be the infinitive plus any phrase or clause associated with it, for example, to speak frankly, to see the difference.
In the sentence infinitive clause as the Parenthesis uses verbs that denote:
Perceptions of senses (to see, to hear, to feel, to watch, to observe, to notice, to taste, to smell, to sound);
To hear them talk, marriage was a prison and intimacy was inconvenient at best [coca, MAG, 2011].
Wish, intention, emotions (to want, to wish, to desire, to like, to dislike, to hate, to intend, etc.);
While he has only entered the Dippie Hippie once, when it opened, to wish Barbara well in her enterprise, he and his officers make it a point both to watch it and to make Barbara aware that they are watching it [COCA, FIC, 2010].
Mental activity (to consider, to believe, to think, to find, to know, to expect, to suppose, suspect, etc.);
To guide this process, the instructional theory known as scaffolding was used [COCA, ACAD, 2009].
It never crossed Tom-Su’s mind, though, to suspect a trick [COCA, FIC, 2000].
Order, request, permission, advice, compulsion (to order, to ask, to request, to allow, to permit, to advise, to recommend, to cause, to force, to make, to let, etc.);
To permit meaningful interpretation of the results, we designed our experiment to include control conditions in which only the target was viewed and rated [COCA, ACAD, 2002].
Sequence (to begin with, to put it differently, to put it simply, to sum up, to summarize, etc.);
To begin with, I tried approaching singing it with what I would call my full voice, which is a 41-year-old adult woman voice and it destroyed the words [COCA, SPOK, 2011].
Opportunity (to happen, to chance, to occur, to take place etc.);
And they had to drill past the point where the mine collapsed, to happen, to reach to – the men where they’ve been waiting all this time [COCA, SPOK, 2011].
Communication and reports (to say, to tell, to report, to judge, to deny, etc.);
His feet, to judge by the boots, must be outsized, even larger than my own [COCA, FIC, 2010].
To maintain integrity of content, advertisements have always been featured on the outskirts of the Journal’s pages, never within the articles themselves [COCA, ACAD, 2011].
The special place among infinitive clauses which function as Parenthesis in the sentence has such verbs and verb expressions:
Linking verbs don’t function in the same way as typical verbs in showing the action. These types of verbs show a relationship between the subject and the sentence complement, the part of the sentence following the verb. They connect or link the subject with more information – words that further identify or describe the subject. While standard verbs are indicative of action, linking verbs identify a relationship or existing condition. These are sometimes described as performing the function of an equal sign because they provide the connection between a subject and a certain state.
Linking words do not describe the action, but always connect the subject to additional information. The most common true linking verbs are to be, to become and to seem.
There are some of phrases used with the verb to be:
To be acceptable, To be baffled, To be believable, To be clean, To be clear, To be confident, To be contrary, To be convinced, To be convincing, To be correct, To be credible, To be cynical, To be honest, To be devoid, To be effective, To be engrossed, To be fair, To be genuine, To be justifiable, To be serious
The following examples show their usage in the context:
“Kathy and I want them to have a strong sense of themselves, to be confident, to have the capacity to be really happy and sad so that they have feelings and are sensitive to the needs of others, and that they want to make a difference in the lives of people,” he said [COCA, MAG, 1997].
To be fair, this case had the lowest retail cost, and it’s not billed as waterproof [COCA, MAG, 2011].
To be justifiable, the practice must be compatible with self-ownership [COCA, ACAD, 1990].
Other linking verbs are to appear, to turn, to prove, to look, to grow, to remain, to sound and to stay.
To sound polished, your usage needs to be up to date [COCA, ACAD, 2009].
Speaking about infinitival clauses as means of expressing Parenthesis it is worth to mention also such infinitival phrases as to be sure, to be certain, to be likely and to be unlikely. There are some examples of their usage:
The coat is expensive, to be sure, but it’s bound to last longer than a cheap one .