When you use a proper noun as though it were a common noun, you're implying that there is a set of entities referred to by that name.
Are you the Bill Gates?
[Out of the set of people named Bill Gates, are you the one listeners would typically be familiar with?]
No, I'm some other Bill Gates. I'm a plumber who lives in Brooklyn.
[Although my name is Bill Gates, I am not the Bill Gates listeners would typically be familiar with.]
In this example, there's a set of one or more people named Bill Gates. Since the definite article the implies the listener can identify what the noun phrase it marks refers to, the Bill Gates refers to, out of the set of all people named Bill Gates, the one with which the listener is likely to be familiar.
The determiner need not be the definite article. We could instead talk about the many John Smiths of the world, implying a set but not identifying any individual member of that set.
But it gets more interesting. Let's take a look at a more figurative example:
This painting of a young Rembrandt holding up a dead bird as though he were the hunter has troubled art scholars for years.
Here, the indefinite article a implies that this is one of many Rembrandts.
But the set here exists only figuratively, dividing the painter into multiple entities according to age:
- a young Rembrandt [Rembrandt, the painter, when he was young]
- an aging Rembrandt [Rembrandt, the painter, when he was older]
Literally speaking, the set does not exist. But we can nonetheless speak as though it does.
And the same grammar can be used figuratively to describe traits other than age. In this question, we can see Dudley divided figuratively according to behavior or personality:
Mr. Dursley hummed as he picked out his most boring tie for work, and Mrs. Dursley gossiped away happily as she wrestled a screaming Dudley into his high chair.
Here, Dudley is treated as though it were a common noun, signaling a set of Dudleys. Although we only know of one member of this set, we could postulate more:
- a screaming Dudley [Dudley while he was screaming]
- a pacified Dudley [Dudley after his parents have calmed him down]
The figurative set of Dudleys allows us to express an attribute Dudley possesses (belligerence),
just as the set of Rembrandts allows us to express an attribute Rembrandt possesses (youth).
The same mechanism works more literally for the Bill Gates or the many John Smiths, since the sets of one or more people named Bill Gates and John Smith exist in reality. But grammatically, whether it's literal or figurative, it works the same way:
When you treat a proper noun as though it were a common noun, you imply that there is a set of entities referred to by that name.