Learn English – What’s the correct usage of “something of something” and “something’s something”? ‘S and OF

possessives

First of all, I don't know how to correctly call this. Possessive case? Educate me, please. Lol.

I've been confused a long time when using 's and of in different cases when I try to point out the belonging or possession of something. I'm writing or talking and I pause when I have to say that something belongs to someone, and it's pretty annoying stumble always with the same stone. Could you help me to clarify my ideas?

Yes, I've looked at some books and sites, but I'm still doubtful.

Here I'm adding some examples. They're not too numerous though. Some of them are pretty simple, but yet they're pretty confusing for me since I really don't know what's the best way to express my idea.

The house of Mary.
Mary's house.

I know these sentences are both correct. What I'm wondering is what should I consider to choose one option above the other one.

Now something more complicated:

Iron Age
Age of Iron
Iron's Age

By the way, my native language is Spanish.

Best Answer

Okay, there are three forms:

A's B (ex. the car's engine)

B A (ex. a car engine)

B of A (ex. the engine of the car)

The first form indicates "possession". B belongs to A.

Perhaps I need to clarify that the word "possession" here is used very loosely. It could refer to almost any sort of relationship. If I say, "Fred's pencil", I mean the pencil that Fred owns, that belong to him and that he can do pretty much anything he wants with. If I say, "Fred's city", I probably do not mean that Fred owns the city and can do whatever he wants with it. I probably mean something more like, the city where he lives.

The "B A" form indicates a "type". When I say, "a car part", I mean a part that is of type "car". In this case, a part that comes from a car or that is normally used in a car. The difference between this and "B's A" can be subtle, but in general, the "B's A" indicates association with a particular thing, while "B A" indicates an association with that type of thing in general. Like if I say, "This is my car's battery", I mean that it is the battery for this particular car. But, "This is a car battery" means it is a battery intended to be used in a car, but which I am not (presently) associating with any particular car.

So, "the Iron Age" means an age that is associated with iron. Not a particular piece of iron, just iron in general.

"A of B" can be used in place of either of the previous two forms. Sometimes we distinguish by the use of articles, pronouns, or other adjectives. Like, "this is the battery of my car" is the same as "this is my car's battery". Other times we just tell by general context. "This was the Age of Iron" is the same as "this was the Iron Age", but "This was the Era of Napoleon" is the same as "this was Napoleon's Era".

Whether you use the "of" form or one of the other two forms just depends on what makes the sentence flow smoothly. Sometimes a sentence is more clear with one form than the other, or just has a nicer rhythm.

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