why does "a number" take a plural noun

[alkaspeltzar]

I have been wondering why in the sentence:

"A number of adults are employed".....why the verb is plural. According to definitions, isn't a number a total, sum or single thing?

Another example would be:

"One half of the people are outside".....this is the same thing, One half is one portion, so why is it treated as a plural?

Just looking for explanation since I normally do alot of math, and these words usually just refer to a quantity and are treated a single entity.

Thanks for the hlep in advance.

Kevin

[Bennevis]

Well, that's the way it is. The emphasis is placed on what goes after "of".

[5jj]

But note:

A number of adults are employed.
The number of adults employed is falling.

'That's the way it is' is not a very helpful answer - but it's the only one there is sometimes.

[emsr2d2]

The best explanation I can come up with is that "A number" here means a number greater than one. Any number greater than one would attract a plural.

One person is unemployed.
Two people are unemployed.
Three people are unemployed.
A number (unspecified but greater than one) of people are unemployed.

[alkaspeltzar]

okay, emsr2d2 I think I understand now....correct me if I am wrong.

Basically, when one talks about "the number", the emphasis is on just that, therefore it is a singular verb.

When one talks about 'a number", it is vague and general. Could be a number greater than 100, or less than that. But either way, that noun " a number" refers to and attracks the plural becuase it is has to do with 'how many', so the emphasis goes on the following plural noun and it uses a plural verb.

From everything being stated and looking in dictionaries, that seems to make the most sense.

[Bennevis]

But note:

A number of adults are employed.
The number of adults employed is falling.

'That's the way it is' is not a very helpful answer - but it's the only one there is sometimes.

I, certainly, overlooked that usage. What I had in mind is the usage dealing with "a number of".