What’s the un­der­ly­ing gram­mar be­hind start­ing off a ɢᴇʀᴜɴᴅ clause with an ᴏʙ­ᴊᴇᴄᴛ pro­noun?

Yes­ter­day I en­coun­tered this sen­tence (I’ll re­fer to the num­bered words in my ques­tion be­low):

This is be­cause many stu­dents think that all of their sen­tences need to be ‘com­plex’ (they don’t!) and¹ them² not un­der­stand­ing³ what a ‘com­plex’ sen­tence is.

I just can't un­der­stand the gram­mat­i­cal con­struc­tion af­ter the link­ing word, and¹.

Why did the writ­er use the ‑ing form³ of the verb af­ter an ob­ject pro­noun them²? And why did he start a sen­tence with an ob­ject pro­noun in the first place?

Source: https://www.ieltsadvantage.com/2015/03/27/ielts-writing-complex-sentence/

Solution 1:

This sen­tence:

This is be­cause many stu­dents think that all of their sen­tences need to be com­plex and them not un­der­stand­ing what a com­plex sen­tence is.

is apt to pro­voke gram­mat­i­cal con­fu­sion be­cause you aren’t ini­tial­ly cer­tain about what two syn­tac­tic con­stituents (call them X and Y) which the con­junc­tion and is co­or­di­nat­ing. The val­ue of con­stituent Y fol­low­ing the con­junc­tion is al­ways the same (“them not un­der­stand­ing what a com­plex sen­tence is”), but ex­act­ly what X is varies in length. Is it (1) need X and Y, or is it (2) think that X and Y, or is it (3) be­cause X and Y?

Here are those three pos­si­bil­i­ties:

1. This is be­cause many stu­dents think that all of their sen­tences need X and Y:
   
   This is be­cause many stu­dents think that all of their sen­tences need (X=to be com­plex) and (Y=them not un­der­stand­ing what a com­plex sen­tence is).

2. This is be­cause many stu­dents think that X and Y:
   
   This is be­cause many stu­dents think that (X=all of their sen­tences need to be com­plex) and (Y=them not un­der­stand­ing what a com­plex sen­tence is).

3. This is be­cause X and Y:
   
   This is be­cause (X=many stu­dents think that all of their sen­tences need to be com­plex) and (Y=them not un­der­stand­ing what a com­plex sen­tence is).

The clos­est to a cor­rect parse is the third one, which it takes your brain more time to work out for sev­er­al rea­sons. One rea­son is be­cause it’s the longest pos­si­ble val­ue for X, so your men­tal pars­er back­ing up to find some­thing that makes sense hits the two short­er pos­si­bil­i­ties first be­fore it comes up­on the cor­rect choice.

Another rea­son is be­cause of be­cause not ac­cept­ing a noun phrase com­ple­ment with­out the prepo­si­tion of. So nev­er just “be­cause not un­der­stand­ing”, on­ly ever “be­cause of not un­der­stand­ing”. (Cred­it to Janus for notic­ing this.)

The last rea­son is that the two con­stituents be­ing co­or­di­nat­ed here are not quite the same thing: X is a fi­nite verb clause but Y is a non-fi­nite verb clause. This is con­tribut­ing to your oth­er con­fu­sion, since the sub­jects are no longer in the same case. Fi­nite verbs have manda­to­ry sub­jects that when they’re pro­nouns are in the sub­ject case (like I, he, them).

But the op­tion­al sub­jects of non-fi­nite verbs, when pro­nouns, can­not be in the sub­ject case. They have to be in the ob­ject case (like me, him, them) or in their pos­ses­sive de­ter­min­er forms (my, his, them).

So that’s what’s hap­pen­ing here: them is the sub­ject of the gerund clause head­ed by the non-fi­nite verb un­der­stand­ing.

It would have been more com­pas­sion­ate if the writ­er had rec­og­nizes the po­ten­tial for con­fu­sion here and slight­ly re­struc­tured the sen­tence to add more sen­tinels to help the read­er parse the sen­tence more eas­i­ly.

Here are a few pos­si­bil­i­ties in that re­gard:

1. This is not on­ly be­cause many stu­dents think that all of their sen­tences need to be com­plex, but al­so be­cause of not un­der­stand­ing what a com­plex sen­tence is to start with.

2. This is be­cause many stu­dents think that all of their sen­tences need to be com­plex and be­cause they don’t un­der­stand what a com­plex sen­tence is in the first place.

3. This is be­cause of many stu­dents think­ing all their sen­tences need to be com­plex and not un­der­stand­ing what a com­plex sen­tence is.

Those should all be eas­i­er on the read­er than the orig­i­nal. Once you un­der­stand what was changed in each of them to fa­cil­i­tate com­pre­hen­sion, you will be­gin to see where you foundered in the un­changed sen­tence you first pre­sent­ed.

Solution 2:

In a comment, BillJ wrote:

... and them not understanding what a ‘complex’ sentence is.

There is a structural problem with your sentence (as others have pointed out) but leaving that aside, the answer to your question is that non-finite gerund-participial clauses take accusative and genitive subjects. In your example, the pronoun is subject of the non-finite clause "them not understanding what a complex sentence is", so the subject could be either accusative "them" or genitive "their".

Solution 3:

The overall structure of your example is: [S this is because S ], by which I mean that the whole thing, [S ... ], is a sentence S, and within that S is another S after "because". That S after "because" is [S many stu­dents think that all of their sen­tences need to be com­plex and them not un­der­stand­ing what a com­plex sen­tence is ].

Working our way down in the structure, this S seems to begins with an S "many students think that all of their sentences need to be complex" followed by "and". If so, we can appeal to a general principle about "and" to identify the structure of the rest. That principle is that "and" (together with other coordinate conjunctions) is preceded and followed by phrases of the same type, and that the entire phrase formed is itself a phrase of that very same type.

It follows that "them not understanding what a complex sentence is" must be an S, but that is a problem here, because what precedes the "and" is a finite (tensed) clause "all of their sentences need to be complex", while what we have here is not like that. As it stands the example appears to be unacceptable.

One way to repair the grammatical problem is to substitute the related finite clause [S they don't understand what a complex sentence is ]. Then, we'd have:

This is be­cause many stu­dents think that all of their sen­tences need to be com­plex, and they don't un­der­stand­ what a com­plex sen­tence is.