The infinitive as parenthesis is used with to. It is generally a set phrase, such as to tell the truth, to be quite frank, to say the least, to put it mildly (crudely), so to speak, strange to say, to make matters worse, to begin with, to cap smth., to be honest, to cut a long story short etc.
The place of the parenthetic phrase in the sentence is not fixed though it is usually placed at the beginning or sometimes at the end of a sentence. In writing it is marked off by a comma:
To be perfectly frank, you are a bad driver.
To be fair, he wasn’t entirely to blame.
To cut a long story short, we said ‘No’.
To make matters worse, it began to rain and soon we got wet to the skin.
Strange to say, he has never been in the theatre.
To put it at its simplest, he believed in Nature.
To cap misfortune, the postman brought him five returned
He is acting rather rashly, to say the least.
When they found out I was not one of them, so to speak,
they ignored me.
Form and Use
The form of a verb ending in –ing is sometimes called (a) the present participle and sometimes (b) the gerund, depending on whether it is used (a) more like a verb or adjective or (b) more like a noun. Thus, whereas the participle is a verbal adjective, the gerund is a verbal noun. In fact, the distinction is not really as simple as this, and some grammarians prefer to avoid the terms participle and gerund.
Simple reading being read
Perfect having read having been read
Functions of the Gerund
A. The gerund has most of the characteristics of a noun. Thus, it can be:
1. The subject of a sentence:
Beating a child will do more harm than good.
The reading of the will took place in the lawyer’s office. Note that when the gerund is used with an article, it cannot usually have a direct object.
The gerund is used in short prohibitions:
No smoking. No parking. No fishing.
But these cannot be followed by an object, so prohibitions involving an object are usually expressed by an imperative:
Do not touch these wires. Do not feed the lions.
2. The complement of a sentence:
To keep money that you have found is stealing.
Seeing is believing. 3. The object of a sentence (see 110): I remember seeing him. She likes dancing.
4. The object of a preposition (see 112):
She is very fond of dancing.
He left without saying anything.
The only part of a verb that can be the object of a preposition is a gerund.
B. But the gerund has some characteristics of a verb. 1. It can take a direct object:
His hobby is collecting stamps.
Meeting you has been a great pleasure. 2. It can be modified by an adverb:
She likes driving fast.
Speaking English fluently needs a lot of work.
C. The gerund can be a noun modifier:
A walking stick a swimming pool a reading room
Note the difference in meaning between the participle as a modifier and the gerund as a modifier:
PARTICIPLE a dancing bear (=a bear which dances), a sleeping child
GERUND a dancing teacher (=a teacher of dancing), a sleeping carriage