# Question one: isn't it time, or isn't it *the* time?

We always say *it's time*, not *it's the time*:

> **It's time**.  
> **It's time** I went home.  
> **It's time** for you to go to bed.  
> **It's time** you started eating right.  
> **It's time** for some fun!  

We can turn all of these into questions:

> **Isn't it time**?  
> **Isn't it time** I went home?  
> **Isn't it time** for you to go to bed?  
> **Isn't it time** you started eating right?  
> **Isn't it time** for some fun?  

And yours fits this second pattern:

> **Isn't it time** you stopped acting the goat?

It would be unidiomatic if you inserted *the*.  People might not understand you.

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# Question two: acting the goat, or acting *like* the goat?

This is an English idiom, and you can find it in [dictionaries](http://idioms.thefreedictionary.com/act+the+goat):

> to behave in a silly way, sometimes in order to make people laugh Insecure and lonely, he resorted to acting the goat to get people's attention. 

You're right that *acting* would normally be followed by *like* today.  But it's not ungrammatical to say it without *like*, and I suppose when this idiom was formed, it may have been more common to use *act* this way.  But in any case, since it's an idiom, you shouldn't change it by inserting *like*.

Why do I say it's grammatical?  Well, you can *act silly*, which shows us that *act* is a verb like *be*, *become*, or *grow*.  Since it can take an adjective, we can tell these verbs take "predicative complements" (PCs) rather than objects, like most verbs.  (We can tell this because objects can't be adjectives.)  So just as you can say *being the goat*, you can say *acting the goat*.

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# Question three: the goat, or a goat?

Again, it's an idiom, so you shouldn't change it.  Otherwise people won't understand!

But why *the*?  Presumably it's the same reason we say *playing the fool*.  We're not talking about any actual fool, nor any actual goat.  We're referring to the qualities of a generic or archetypical fool or goat.

(Though, to be honest, I have no idea what makes that goat-like.  It's a pretty weird idiom!)

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# Notes

*Note one*: the subordinate clause *you stopped acting the goat* is in the past tense, but it doesn't indicate **past time**.  Instead, it indicates **counterfactuality**.  In *The Cambridge Grammar of the English Language*, this use of the past tense is called the **modal preterite**.

*Note two*: *Play the goat* is a fairly unusual idiom.  It was chosen, I think, to translate the original French idiom *faire le zouave*, which is fairly silly.