At the age of and at a speed of

[Nonverbis]

Could you speculate on the subject why:

at a speed of 100 kph/50 mph

He left school at the age of 18.

(https://www.oxfordlearnersdictionaries.com/definition/english/age_1?q=age).

The article is what is interesting here.

Maybe your speculation could help me memorise this. Or maybe there will occur a mnemonic hint or something.

 

[Tarheel]

I'm having a hard time figuring out what your question is.

"He left school at the age of eighteen" means he left school when he was eighteen. (I don't think that's what your question is about though.)

 

[Tdol]

You can say at the speed of in some contexts- at the speed of sound.

 

[Nonverbis]

I'm having a hard time figuring out what your question is.

"He left school at the age of eighteen" means he left school when he was eighteen. (I don't think that's what your question is about though.)

The point why in one case there is the definite article ant in the other case the indefinite one.
Though the language cunstruction by its nature and form is the same.

 

[emsr2d2]

The point is that I want to know why in one case [STRIKE]there is[/STRIKE] the definite article is used [STRIKE]ant[/STRIKE] and in the other case the indefinite [STRIKE]one[/STRIKE] article, even though the [STRIKE]language[/STRIKE] construction is, [STRIKE]by its[/STRIKE] in nature and form, [STRIKE]is[/STRIKE] the same.

Articles and prepositions are difficult! They're probably the hardest things to master for learners of English. Sometimes you just have to memorise the correct usage as you stumble across it in your reading.

 

[Nonverbis]

You can say at the speed of in some contexts- at the speed of sound.

I've read about that in a dictionary. And this is logical. As the speeds of light and sound are constants.

But the constructions in the question are not logical at all. As for me.
So, that's why I ask you: maybe there is some logic here.

It can happen that I can't see this logic because of cultural differences.

 

[Tarheel]

Try:

I read that in a dictionary. The speed of sound and the speed of light are constants. But the constructions in question are not logical st all.

Maybe not. But we're talking about language, not logic.

It's better, I think, not to insist that language be logical. Why? Because that won't make any difference. Just get used to whatever usage you're trying to learn.

 

[Alexey86]

So, that's why I ask you: maybe there is some logic here.

You might find this thread helpful: https://forum.wordreference.com/threads/at-a-the-speed-of.1660429/