I began reading the book.(g)

He went in reading his book.(p)

First of all, Participle I expresses an action as characterizing a person or thing (like an adjective) or as modifying another action (like an adverb). The gerund expresses an action in its most general sense, actually naming it, and looks more like a noun. Participle I gives qualitative characteristics to the subject: his speech was thrilling. The gerund identifies the subject by revealing its meaning: One of hobbies is drawing caricatures.

The participle testing includes the adjective \ adverb substitution backed by the question. If we take the sentence He was in a terrifying condition and ask the question What kind of condition was he in? we will see that we can replace the word terrifying by the adjective awful, for example. The participle also enters into easy coordinative relations with adjectives: That was a false but convincing show of affection.

Some linguists think that the difference between the gerund and participle I can be illustrated by 2 different types of convertion. The gerund is subject to the noun convertion; while the participle – to the adjective convertion. Your airing (g) the room – To take an airing (noun). Animals living (p) in the jungle – Living languages (adjective).

Moreover, the gerund can function as subject and object. Participle I – as attribute and adverbial. Swimming is my pastimes for holidays. (subject) Feeling tired and having nothing more to do, Jude sat down on one of the sofas. (adverbial)

In the attributive function, the semantic differences between participle I and the gerund are unquestionable: the noun modified by participle I denotes the actual doer of the action, and the participle denotes its processual qualification; the meaning of the gerund in the attributive function is non-dynamic; the difference can be demonstrated in the following tests, cf.: a sleeping girl à a girl who is sleeping (participle I); a sleeping pill à a pill taken to induce sleep (the gerund).

 

However in certain syntactic contexts the difference between the gerund and participle I tends to obliterate. For example, I felt annoyed at his failing to see my point at once. (gerund) I felt annoyed at him failing to see my point at once. (neither the gerund nor the participle). This usage presents a case known as half-gerund. The half-gerund has as its subject word a personal pronoun in the objective case. Such cases are common with:

-nouns accompanied by attributes in postposition: Do you know any other woman buying a dress like that.

-to avoid ambiguity which might occur in oral speech if the gerund is connected with a noun in the possessive case: I cannot imagine his son marrying so young.

-when the gerund is preceded by more than one noun: She objected to children and women smoking.

-when you want to stress the person component of the complex: I hate the idea of you wasting your time.

So the half gerund is somewhere in between the gerund and Participle I.