Compound subject whose parts are joined by "and" and verb agreement : when is the singular correct? [duplicate]

Question

I am in doubt as to whether the subject-verb agreement of the second sentence of this paragraph is correct :

Unfortunately, there is no such thing as the ideal home workshop because most people are limited by the space available and by their budget.

However, the information and diagram here acts as a guide to help you formulate a sensible workshop layout and a machinery “wish list”.

I suppose if the compound subject is seen as a single unit, then the sentence can be considered as correct.

A little further in the same book, another sentence has a singular verb with a compound subject :

Alternatively commandeer a garage, or build yourself a substantial workshop if outdoor space and permission allows – however, do consider the impact of machinery noise on your neighbours.

Can "outdoor space and permission" be seen as one thing, or would this be considered a mistake ?

Answer 1

I would only treat a compound subject "X and Y" as singular if it were a compound phrase that very often occurs together and which people conceptualize as a single thing. For example, I might say "this rod and reel is all tangled up", or "that mortar and pestle is for sale", or "my gin and tonic is not strong enough".

In the examples you cite here, I would consider those verbs incorrect, as far as agreement with the subject. It would be more correct to say "the information and diagram here act as a guide...", and "outdoor space and permission allow..."