Was "their being followed" replaced by "they're being followed" over the years?

Question

I was reading A Study in Scarlet yesterday and noticed the following sentence:

They must have thought that there was some chance of their being followed, for they would never go out alone, and never after nightfall.

I'm not a native English speaker, when I first saw "their being" I thought it was a typo, and the correct spelling would be "they're [they were] being followed", then I realized the word being was actually the noun, not the verb, that made sense, but I couldn't recall ever seeing this "version" of the expression used. I mostly see "they're being followed", "he's being followed", etc.

With the story being over 200 years old (first published 1887), I assumed this was an old expression that was replaced in later years with the common "they're being", Google Ngram viewer shows a general decrease in use of "their being followed" over the last 300 years, vs a slight increase of "they're being followed" since the 1960's, with the latter form overtaking the former during the mid-1990's.

My question is, is the latter form basically a "mistake" emerging from a typo that was later "accepted"? Or was this caused because th common usage of the word "being" changed from a noun to a verb over the years?

Answer 1

This is not a mistake and it is perfectly fine to use such expression even in the modern days (it is more common to see it in formal writing though). In short, there is nothing wrong with having a verb in gerund form be used after a possessive determiner.

Here is an extract from a Wikipedia article.

Gerunds preceded by a genitive

Because of its noun properties, the genitive (possessive) case is preferred for a noun or pronoun preceding a gerund, which is functioning as the subject of the gerund's verbal element.

We enjoyed their [genitive] singing.

This use is preferred in formal writing or speaking. In casual speech, the objective case is sometimes used in place of the possessive:

I do not see it making any difference. (I do not see its making any difference is correct.)

Using the possessive case with the gerund is applicable in all situations. For instance:

He affected my going there.

He affected your going there.

He affected his/her/its going there.

He affected our going there.

He affected their going there.

He affected Mary's going there.

The verbal action of the gerund belongs, in effect, to the subject practising it; thus, the possessive is required to clearly demonstrate that relationship.

In some situations, either the possessive or the nominative case may be logical, but with slightly different meanings; but when the nominative case is used the verbal element is a participle, not a gerund:

The teacher's shouting startled the student. (Shouting is a gerund, and teacher's is a possessive noun indicating whose shouting is being talked about; but shouting is the subject of the sentence.)

The teacher shouting startled the student. (Shouting is a participle describing the teacher. This sentence means The teacher who was shouting startled the student. In this sentence, the subject is the teacher herself. A clearer way to write this sentence might be The teacher, shouting, startled the student.) Either of these sentences means that the student was startled because the teacher was shouting, but the first places greater emphasis on the shouting by making it the subject of the sentence, while the second places greater emphasis on the teacher and is not using a gerund.

Despite such examples of a similar construction that uses a participle instead of a gerund, using a noun or pronoun in anything except the possessive case as the subject of a gerund (He affected me going there) is incorrect in formal writing.

However, the usual accusative is a less formal alternant. In a few situations, the genitive becomes redundant. For instance,

He objected to the girl being appointed the President. (Alternatively, He objected to the girl's being appointed the President.) We were delighted at Paul being awarded the prize. There is no chance of the snow falling. (Not, There is no chance of the snow's falling.)

[updates]

The expression of they're being followed is simply not grammatical. Either use of them or of theirs, remove the of, or replace it with that.

Answer 2

The language hasn't changed, and there's no mistake here. The key is the word of.

Doyle could have written:

There is some chance they're being followed.

however, with the preposition there, that would not read right:

There is some chance of they are being followed.

The correct way to say that would be:

There is some chance of them being followed.

Look what happens to your Ngram when the word of is included in the two expressions:

As for why the numbers are decreasing, I think that's simply due to the fact that there were very few instances to begin with. When the vertical axis has numbers as small as 0.00000012%, it doesn't take too many additional instances of the expression before the number found by Google books doubles or triples for a certain year.