“as much as” vs. “as much as is”"

Question

In a textbook, I read this sentence:

Stretch your arms as much as is comfortable for you.

But can you say it without the is?

Stretch your arms as much as comfortable for you.

Is there any difference?

Answer 1

No doubt a sentence shouldn't be longer than clarity requires—but what does clarity require? If I encountered the sentence "Stretch arms as comfortable" in a series of instructions written in a clipped telegraphic or outline style, I would interpret it to mean "You should stretch your arms as much as is comfortable for you to do"; but getting from the short form to the long one would take me a little while, and it would involve some risk of misinterpretation.

Obviously, different word omissions have different effects on the flow of a sentence. Anyone accustomed to reading English sentences will recognize the imperative form of the opening words "Stretch your arms" and won't pause at all to supply the absent "You." Likewise, most English readers are so accustomed to completing truncated sentences of the type "Stretch your arms as much as is comfortable for you" that the absence of "to do" at the end of the sentence is no impediment to understanding; indeed, the words "for you" (which the sentence does include) are likewise expendable without any loss of pace.

To my ear, then, the original sentence remains completely and immediately coherent when expressed as "Stretch your arms as much as is comfortable." I read it, I understand it, and I haven't slowed down a bit.

The omission of "is" from the sentence, however, affects me differently: I pause for a couple of beats to identify and restore the missing word before I feel that I fully understand the sense of the sentence. Other readers may take the omission in stride, but I would be surprised to discover that I'm the only one who finds it distracting.

The time loss involved is quite brief, but it's not insignificant, especially if the author hopes to maintain rhythm and pacing across a longer piece of writing. Moreover, if the author tends to drop such arguably nonessential words as the "is" here regularly, easily distracted readers will have to pause more often, which cumulatively can render the prose unduly burdensome to read.

Ultimately, if "Stretch your arms as much as comfortable for you" takes a significant number of readers slightly longer to make sense of than "Stretch your arms as much as is comfortable for you" does—even though the sentence is one word shorter—what has the author gained by dropping the word? Nothing desirable, I think.

Answer 2

Yes, both are correct and grammatical. No, there is no difference, except that one is shorter, which is the principal reason for the variation.

The is is mandated by the grammar, leaving some clause structure behind while deleting the degree phrase in

• [You] stretch your arms
  [to the maximum degree D, such that]
  [your stretching your arms to degree D] is comfortable for you.

In the above, the [You] understood is deleted, the bracketed degree phrase becomes as much as, and the bracketed subject complement clause is simply deleted as repetition.

The is that gets left behind, however, is predictable and thus contributes no information; coming immediately after the phrase as much as (which is certainly enough to mark the construction), and resembling as, is often gets deleted.

That's all.
The more in a hurry one is, the less likely one is to dot all the syntactic i's and cross all the t's.