Let’s conclude our lesson on subjects which may seem plural because two items are mentioned but which in grammatical terms are singular because only one of the items mentioned is preceded by an article (the or a/an) or a determiner (my, his, your, our, her, their, etc).
So the following expressions are all singular, grammatically speaking:
My friend and teammate
His brother and friend
The teacher and coach
A coach and player
A minister and MP
Our friend and neighbour
My brother and sister
Your mum and dad
A friend and confidant
Being singular, these expressions must agree with singular verbs for the sentences to be grammatically correct, as in:
Our friend and neighbour has agreed to accompany us to the mall.
Your mum and dad is here to see you.
My brother and sister leaves for school tomorrow and so I’m going to be lonely.
A minister and MP wants my services as a secretary.
As you know, if you have two people in mind in all the above expressions, then the correct thing is to precede both persons with an article or a determiner, so that they can become plural, grammatically, for them to agree with plural verbs, as in:
Our friend and our neighbour have agreed to accompany us to the mall.
Your mum and your/her dad are here to see you.
A minister and an MP want my services as a secretary.
My brother and my sister leave for school tomorrow and so I’m going to be lonely.
The teacher and the coach are in charge of the trip outside the school.
While it is easy to see a minister and MP as one person (that is, a minister who is also an MP), it may be difficult to perceive my mum and dad or my brother and sister as one person.
But you must understand that if one has a single parent, perhaps as a result of the other parent passing on or being irresponsible, one can refer to one’s mum, for instance, as my mum and dad (that is, my mum who doubles as my dad) because my mum does what my dad should be doing for me, in addition to her motherly responsibilities.
It is the same for the expression my brother and sister — I have only one sibling and he or she doubles as a brother and a sister at the same time.
That is why I can write or say:
My brother and sister has come to pick me home.
But bear in mind the fact that if we are talking about two people, we must indicate so by using the determiner before both brother and sister, as in:
My brother and my sister have come to pick me home.