enable or enables?
This is an example I have read from an English teaching material

"...the English speaker has at his disposal a vocabulary and a set of grammatical rules which enables him to communicate his thoughts and feelings, in a variety of styles, to another English speakers."

It is pointed out that "enables" should be " enable" because it aligns with grammatical rules instead of a vocabulary. However, isn't the subject of the this clause "a set of grammatical rules"?

which one is correct? Thanks.

Question

enable or enables?
This is an example I have read from an English teaching material

"...the English speaker has at his disposal a vocabulary and a set of grammatical rules which enables him to communicate his thoughts and feelings, in a variety of styles, to another English speakers."

It is pointed out that "enables" should be " enable" because it aligns with grammatical rules instead of a vocabulary. However, isn't the subject of the this clause "a set of grammatical rules"?

which one is correct? Thanks.

Answer

Personally, I would interpret this sentence as having "a vocabulary and a set of grammatical rules" at the head of the clause: two things, meaning the verb should be "enable".

...the English speaker has at his disposal [[a vocabulary and a set of grammatical rules] which enable him to communicate his thoughts and feelings...].

(Also Gary is right about "another English speakers")

Answer

To me, it is a mistake, and it should be 'enable'. Is that what you mean by 'it is pointed out'? 
To me, the object is '...vocabulary and ... rules'.
I suggest you get a newer book though. The style of that language is rather archaic, as is the sexist 'he/his'. It reads as if it were written 50-100 years ago.
There is another error as well. 'another English speakers'. It should be 'other English speakers' or 'another English speaker'.

Answer

I thought it referes to both of them, hence plural. Does it align?
A and B enable me to Y.
A and lots of Bs enable me to Y.
A enables me to Y.
A set of As enables me to Y.
I guess in the last one, enables connects to a set as you say, being singular.