comparative constructions - You're taller than (is/are) described

You're taller than described.

I think 'be' is omitted between 'than' and 'described', right?

If so, what's the correct form of 'be'?

a. You're taller than are described.

b. You're taller than is described.

And why?

Answer

In a comment under the question, you said:

If the omitted subject is 'you' I don't see why 'are' is not possible.

The verb for of to be would be are if it followed the subject you. Except that it doesn't. In this case, the verb described (barring further context that isn't known from the sentence alone) doesn't have an explicit subject.

We can't assign the act of description to anybody (singular or plural) because the sentence doesn't say who is describing the thing, either directly or indirectly. Because there is no explicit subject, the subject becomes the dummy subject it. In other words:

It is described that you are a certain height.

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While the to be has been omitted from the original sentence, so has this subject. In other words:

You're taller than described.
→ You're taller than is described.
→ You're taller than it is described.

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There is a way in which you could use you are, but it would require a longer form of sentence:

You're taller than you are described (as being / to be).

But we can't omit the second you without it sounding unnatural—because the assumption (from normal speech) is that the shorter version is a short form of the dummy subject form of sentence. (And it are would be wrong.)

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It's also possible to remove the dummy it altogether by changing the verb to a noun:

You're taller than your description.

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However, if we knew from context that it was you who had provided the description, then the sentence would not use the dummy it—but it would still be different than you suggest.

It would be something like one of the following:

You're taller than you described.
You're taller than you had described.
You're taller than you describe.
You're taller than you have been describing.

In all of these cases, the repetition of you is necessary in order to distinguish it from the dummy subject version.