Comparative adverbs

"Officially" (or so I believe) English doesn't have comparative adverbs (a single word rather than "more" + an adverb), but faster is in common usage as one, for example:

Do it faster

When strictly speaking one should say:

Do it more quickly

Is the former an error in grammar? Or has English (d)evolved to such an extent that faster may be used as a comparative adverb?

Solution 1:

I don’t know where this myth got started, but adverbs and adjectives form inflections by degree in precisely the same way. There is no difference at all.

• They pushed harder, faster, and deeper that day than ever before.
• Our team worked hardest.
• Their drill delved deepest.

And it isn’t even the case that there is some rule that somehow exempts ‑ly modifiers — be they adjectives or adverbs, it doesn’t matter — from inflections of degree. They take either more or -er for comparatives, and either most or ‑est for superlatives. Watch:

• I showed up earlier than he did.
• I got here earliest.
• He got here later.
• I have curlier hair than you.
• One is the loneliest number you’ll ever know.

Also, onliest has a long history, although it is now mostly confined to dialect.

And there is absolutely nothing whatsoever with saying:

• He ran faster than any of us that way.

No one, but no one, can ever say a word against against it.

Edit

Here are more examples of comparative adverbs.

Given that this is an adverbial use:

A man walks clean if in a foul way he contract but a few spots of dirt.

Can he then not walk cleaner? Similarly here:

The riches of the East expended that they might sleep soft and wake in magnificence.

Can they not sleep softer that way?

Consider this laughter:

I shouted ‘hurrah’, and laughed loud and long.

Can I not laugh louder and longer?

Can a joke that falls flat, if retold, fall flatter?

If one day you’re sitting pretty, and things get even better the next day, couldn’t you be sitting prettier?

Could you not be harder-pressed to do something today than yesterday?

Consider these adverbial uses of dear:

• 1807 Byron Ho. Idleness, To E. N. Long 99 ― The dear-loved peaceful seat. I shall soar higher tomorrow than today.
• 1822 Scott Pirate xix, ― That knowledge, which was to cost us both so dear. & 1833 Ht. Martineau Cinnamon & P. vii. 124 ― It must do without some articles··or pay dear for them.

If you paid dear yesterday, and dearer today, and paid dearest tomorrow, those are all normal inflections.

I could go on all day, but surely it is clear by now that there has never been any general “rule” forbidding inflecting adverbs by degree.

(Sure, there are some adverbs that you just don’t do that with, like now for example, but that is a wholly different matter. It is hard to be “nower” simply because now does not readily admit inflection by degree. But even for that one, you could probably put together a situation where it would somehow be understood.)

Solution 2:

"Officially" English does not have comparative endings for adverbs ending in -ly. However, as the comments show, there are plenty of official adverbs that do not end in -ly and actually look like adjectives. These are called flat adverbs, and they do have comparative and superlative morphological endings. Hard, harder, hardest, for example. They used to be more common, but around the end of the 19th century grammarians decided it was for the best if we differentiated adverbs by giving them their own suffix (-ly) that does not change in comparative form.

To give you an idea of the increasing rarity of flat adverbs, consider some of these ear-straining uses that were quite common before the 20th century but have have since died out:

• "tottering on his fore feet, for he was powerful tired"
• "yet Jonah was exceeding glad"
• "And, O, wondrous precious blood"

However, don't tell anybody from New England about this or they'll give you a wicked hard smack upside the head.

In terms of your two examples, depending on what "it" refers to, we might prefer fast over more quickly.

A person might "drive faster" if we were referring to the speedometer, and she might "drive more quickly" if we were referring to her knack for finding shortcuts home.

Some hard line prescriptivists might chide you for using "faster" instead of "more quickly" in a case where both could fit, but that's just preference. You have the dictionary on your side. For now. However, there are lots of instances of where a flat adverb will not do and you will need an -ly adverb. For instance,

I love you deep (no)

I love you deeply (yes)

And the other way around,

Stand close to me (yes)

Stand closely to me (no)

An easy way to know if an -ly adverb is called for is if the adverb answers the question "how?" As for when it's okay to use a flat adverb, this site says "they’re most often suitable for brief imperative sentences."

Hopefully this helps answer your question.