Now coming back to your query: usage such as decrease in may be followed by a complex gerund ( noun out, noun in), but not a simple gerund (noun out verb in).

Can you explain exactly when "decrease in" cannot be followed by "demanding"?

thangvietnam

In order to answer your query, I would have to first clarify that there are 2 types of gerunds:

First note that all gerunds are nouns. The two types of gerunds are as follows:

Simple gerund: Noun out, but verb in

Raising the national flag on independence day is a norm in our school.



Here raising is a simple gerund. If you look inside the phrase containing the gerund raising the national flag, you would notice that the verb function is more prominent than the noun function; i.e. you could easily use the phrase as a full working verb: I am raising the flag.

Complex gerund: Noun out, noun in.

The raising of the rebel flag indicates the downfall of the regime.

Here raising is a complex gerund. If you look inside the phrase containing the gerund The raising of the rebel flag, you would notice that the noun function is more prominent than the verb function; i.e. you cannot easily use the phrase as a full working verb: I am the raising of the rebel flag... senseless.

How to distinguish complex gerunds from simple gerunds? A complex gerund generally has an article, and in some cases an adjective, preceding it and a preposition after it. Following is an example from MGMAT SC strategy guide:

Tracking satellites is important for space agencies: simple gerund.
The accurate tracking of satellites is important for space agencies: complex gerund.

Now coming back to your query: usage such as decrease in may be followed by a complex gerund ( noun out, noun in), but not a simple gerund (noun out verb in).

In the above example demanding is a simple gerund and hence cannot be used after decrease in.

However the following usage is correct:

There has been a decrease in the spending of the consumers.

Here spending is a complex gerund.

A Gerund is a verb taking the ‘ing’ form and, functioning essentially as a
noun. A gerund may be followed by more descriptive words such as adjectives, prepositions or objects of prepositions and in such they are called gerund phrases

Example

"Feeling gratitude and not expressing it is like wrapping a present and not giving it." ---- An old saying.

Here the words feeling, expressing, wrapping and giving are examples of gerunds.

Gerunds and Present Participles

Present participles also take the ‘ing’ form. However a present participle functions as a non-finite form of a verb phrase, In contrast, gerunds behave like nouns.

How to differentiate a gerund from a present participle or from part of a progressive tense verb .

Let us take a simple verb sing; its ‘ing’ form is singing. It can be either a present participle or a gerund or can be part of a past or present progressive tense.

1. Progressive tense

When a verb+ing word is preceded by an auxiliary verb, then it becomes a verb, indicating the tense.

Am singing
Is singing
Was singing
Were singing
Have been singing
Has been singing
Had been singing
Will be singing

2. Present participle

When the verb+ing form or its phrase acts an adjective, modifying a noun, then it is a present participle.

Singing a song, Tom walked along the river.
Shouting abuses, Dick tried to browbeat Harry
By sending a bouquet, the students expressed their love for their teacher.

Here, the ‘ing’ forms modify a noun that is placed next to the comma. These are all participles.

3. Gerund

On the contrary, when the ‘ing’ form is followed by a verb or verb phrase then it will be a gerund.

Going by his words will lead to wrong conclusions
Shopping on week- ends is cumbersome because of heavy crowds.

4. A gerund is essentially a noun trying to do an action. We can apply some of the attributes of a noun and see whether the ing form fits within the parameters of the noun.

4A. The first such test is whether the ing form acts as a subject or object.

Singing is a pleasant entertainment

Here singing is the subject of a simple sentence; only a noun or a noun phrase can act as the subject of a clause. Hence, in the given context, ‘singing’ is a gerund

4B. See whether the ing form is an object of the verb

Tom likes singing
Singing is the object of the verb ‘is’; it is a gerund

4C. see whether it has any adjective preceding it, especially in the form of a possessive pronoun

Tom feels that his singing is better than that of many others

Here the verb+ing form singing is modified by the possessive pronoun ‘his’. Hence, singing is a gerund.

4D.Sometimes an article is a gerund - marker. See whether the ing verb is preceded by an article such as ‘the’
‘The shopping’ at the Spencer’s is a delight.

4E. See whether the ing word can be replaced by the word ‘it’ and the sentence still completes the meaning. The pronoun ‘it’ can complete the meaning while a participle cannot.

Singing is a good past time

Here we can replace singing with the pronoun it – It is a good past time.

4F... see whether the ing word or the entire ing phrase can be replaced by the word ‘something’

Singing along the riverbank, Tom jogged for nearly four miles in one hour
(Singing) Something along the riverbank, Tom jogged for nearly four miles in one hour

(Singing along the river bank) Something, Tom jogged for nearly four miles in one hour

When you replace the ‘ing’ word or phrase with something, nothing meaningful turns out. Therefore, the phrase starting with singing cannot be a gerund.

Now try this.

Signing along the riverbank is a refreshing pastime

After replacing the ‘ing’ word with something, the sentence reads as
Something (Singing )along the river bank is a refreshing pastime

Now you can see there is some meaning in the clause. Therefore, the ‘ing’ phrase is a gerund in the context.

EO &E

However, I figured out that demanding is not correct because it was looking awkward. I read your explanation and found it difficult to distinguish where to use simple gerund and where to use complex one just on the basis of emphasis. Is there any other way to figure out where to use simple gerund and where to use complex one? Thanks !!