Rules for nominalizing a verb

Solution 1:

The general rule for creating gerunds is:

In English, the gerund is identical in form to the present participle (ending in -ing) and can behave as a verb within a clause (so that it may be modified by an adverb or have an object), but the clause as a whole (sometimes consisting of only one word, the gerund itself) acts as a noun within the larger sentence. For example: Eating this cake is easy.

The present participle of to arrive is arriving. This is its gerund form. While the noun form of to happen and its gerund are identical, they are not the same thing. They share a form, but the derivation of the gerund is not the derivation of a noun as well. There is a description of the differences here:

Not all nouns that are identical in form to the present participle are gerunds.[3] The formal distinction is that a gerund is a verbal noun – a noun derived from a verb that retains verb characteristics, that functions simultaneously as a noun and a verb, while other nouns in the form of the present participle (ending in -ing) are deverbal nouns, which function as common nouns, not as verbs at all.

OK, so when do you use "-ing" to create a noun? The dictionary entry on the suffix -ing says that -ing is:

a suffix of nouns formed from verbs, expressing the action of the verb or its result, product, material, etc. ( the art of building; a new building; cotton wadding ). It is also used to form nouns from words other than verbs ( offing; shirting ). Verbal nouns ending in -ing are often used attributively ( the printing trade ) and in forming compounds ( drinking song ). In some compounds ( sewing machine ), the first element might reasonably by regarded as the participial adjective, -ing 2 , the compound thus meaning “a machine that sews,” but it is commonly taken as a verbal noun, the compound being explained as “a machine for sewing.”

Now, how do you know how to create a noun from a verb in general?

There is no set rule. As you can see from this list of suffixes, there are many endings that can get tacked onto a word. There are patterns (for example, you add "er" to a verb of activity, like "write" to "writer"), but no hard and fast rule. For reference, the list of noun suffixes which are added onto verbs or adjectives is:

Noun Suffixes

• er added to a verb is used for the person who does an activity: writer, worker, singer,... (sometimes -or, as in actor, sailor, supervisor,...)
• er/-or are also used for things which do a particular job: tin-opener, projector, ...
• er and -ee can contrast with each other, meaning "person who does something" (-er) and "person who receives or experiences the action" (-ee): employer/employee, ...
• (t)ion is used to make nouns from verbs: communication, pollution, admission, ...
• ist (person) and -ism (activity or ideology): marxist/Marxism, terrorist/terrorism, ...
• ist is also used for people who play musical instruments: pianist, violinist, ...
• al is added to some verbs to make nouns: arrival, refusal, ...
• ness is used to make abstract nouns from adjectives: happiness, goodness, weakness, ...
• ment is used to make abstract nouns from verbs: excitement, enjoyment, ...
• hood is used to make abstract nouns, especially family terms, from nouns: childhood, brotherhood, ...
• ship is used to make abstract nouns, especially status, from nouns: friendship, membership, partnership, ...
• (i)ty is used to make abstract nouns from adjectives: honesty, loyalty, ...

Solution 2:

This example helped me to understand that:

I am watering the plant. [watering = verb]

The plant needs watering. [needs = verb and watering = noun/gerund]