In modern German, one can make tief into the comparative tiefer, regardless of whether the word is used as adjective or adverb. In English, I now have a sentence in which I want to do the same thing with the English deep, because more deeply does not suit the cadence of my sentence and, frankly, deeplier looks dippy. Can I do what I want? Can I use deeper as an adverb? Is this good usage? Is it good philology? Is it sanctioned by practice? If so, why, please? If not, why not?

My Webster's Ninth New Collegiate Dictionary surprisingly seems to offer no clue.

I realize that English occasionally allows the positive deep as an adverb, but such usage probably would be pretentious in my particular instance -- or, at best, would serve only to dodge the linguistic question. If such dodging makes bad English in principle, then one prefers not to dodge. It is not that I wish to convert the poetic adverb deep into deeper, but the more pedestrian adverb deeply into deeper.

(I do not know how interesting or relevant my specific sentence is to readers of this site, but if it interests you: "Ideally, the professional mathematician knows or precisely specifies in advance -- or, deeper, reveals the very wisdom of -- the set of fundamental axioms he means to use to derive a result.")

  • Looks like General Reference to me. You can breathe deeply, but you can't breathe deeper unless there's a specified (or strongly implied) less deep breathing being compared against. Commented Sep 8, 2012 at 13:56
  • @FumbleFingers I agree, this looks like general reference, but I cannot find the answer in general reference. Admittedly, my general references are dictionaries, which are probably insufficient for a grammar question. I know that deep is an adverb (dig deep), as well as an adjective (a deep breath). I have used deeper as an adverb ("We need you to breathe deeper"), though perhaps in violation of proper grammar.
    – Mike
    Commented Sep 8, 2012 at 15:36
  • @Mike: Sure, deeper in your example is an "adverb". But it's a comparative adverb - in that case, deeper than normal, or deeper than you're currently breathing. OP's proposed usage is of that general ilk, but as others have said, it's pretty awkward in his specific case. Prsonally, I think his entire parenthetical phrase is both grammatically and semantically a bad fit for the main sentence. And I have trouble working out why he sees knows and precisely specifies in advance as juxtaposable elements within the main sentence anyway. Commented Sep 8, 2012 at 15:47
  • @FumbleFingers I agree entirely. Most importantly, I agree a rewrite would be preferable. I think he wants the superlative rather than the comparative adverb, but because or is used, the implication is that knows and specifies are two equivalent options, whereas I would consider them standard versus good behaviors for the professional. I write such sentences and am quite empathetic with OP.
    – Mike
    Commented Sep 8, 2012 at 16:04
  • @Mike: You're ahead of me then. I'd have thought since our hypothetical mathematician might know the axioms himself, but fail to specify them to others, these two possibilities shouldn't be contrasted using "or" in the first place. And where to you draw the line between "precisely specifies" and "reveals the very wisdom of" (which strikes me as incredibly ungainly phrasing anyway)? Commented Sep 8, 2012 at 16:10

2 Answers 2


You can certainly use deeper as the comparative of the adverb deep. It was good enough for Milton (‘That they may stumble on, and deeper fall’), and for other writers too.

That said, the sentence as a whole doesn’t sound quite right. For one thing, it's unusual to follow wisdom of with a noun in that way, rather than with the -ing form of a verb.

  • To have asked you to rewrite the sentence for me would have been unreasonable. However, since you yourself have mentioned it: I first drafted that sentence a couple of years ago and have never really liked it. It starts to go wrong from its first word. Without spending much of your time, if a rewritten sentence occurred to you to suggest, I should be glad to read it. (For information, in my manuscript, the sentence leads its subsection. Nothing immediately precedes it.)
    – thb
    Commented Sep 8, 2012 at 14:50
  • 4
    Well, only you know what effect you might want to achieve, and you will have a greater knowledge of the subject matter than I have, but you might like to consider something like: ‘Ideally, the professional mathematician will know which set of fundamental axioms he needs to use to achieve the desired result. He may even specify them precisely in advance or, at a somewhat deeper level, explain the rationale behind them.’ Commented Sep 8, 2012 at 15:36
  • I came for advice on adverbs because that is what I had thought that I needed, but it seems that what I really needed was your helpful suggestion to replace my brittle, old sentence! I have copied your rewrite into my draft and am now smoothing it into context. I suspect that the old sentence, which had prompted the question, is a goner.
    – thb
    Commented Sep 8, 2012 at 19:46
  • If your suggestion's issue interests you, an entirely rewritten paragraph has flowed rather naturally from it. It reads much better now. Moreover, I would like to think that I understand, or begin to understand, the kind of change your suggestion represents. Thank you.
    – thb
    Commented Sep 8, 2012 at 21:07
  • Glad that it helps. It's good that you rewrote the entire paragraph to ensure consistency of style. Commented Sep 9, 2012 at 6:14

The comparative and superlative degrees of adverbs follow the same rules in English as those of adjectives do.

As for using deep as an adverb, you can certainly delve deep, and thus delve deeper. If you were using delve deeply, though, you would have to use delve more deeply. That’s because the only time you use a ‑y > ‑ier rule for forming comparative degrees of adjectives or adverbs is when it is a two-syllable word that is not an ‑ly word. (Everything I say in this posting regarding comparatives with ‑er with also applies to superlatives with ‑est.)

  • For example, artsy > artsier, beefy > beefier, bossy > bossier, crazy > crazier, funny > funnier, edgy > edgier, mousy > mousier, phony > phonier, pretty > prettier on the one hand.
  • But on the other hand aptly > more aptly, costly > more costly, coyly > more coyly, dryly > more dryly, gaily > more gaily, grisly > more grisly, hourly > more hourly, idly > more idly, kindly > more kindly, manly > more manly, mildly > more mildly, newly > more newly, simply > more simply, surely > more surely, truly > more truly, wryly > more wryly.

Sometimes in informal speech you will hear ‑ly > -lier in places where the “rule” says it should use the “more ━ly” version instead, like hilly > ?hillier, silly > ?sillier, manly > ?manlier. I’m not even sure those are completely “wrong”.

Note very carefully that in words ending in ‑ly for other reasons than to make a modifier out of another word with an ‑ly suffix, that now again ‑ly > ‑lier for two-syllable words. So for example holy > holier, ugly > uglier, early > earlier, lonely > lonelier.

Note also that only does not normally take inflections, so ?onliest is considered informal.

Also, sometimes two competing forms exist, especially of adjectives, such as friendly > friendlier or more friendly, homely > homelier or more homely, lively > livelier or more lively, sickly > sicklier or more sickly.

Lastly, two-syllable ‑ey words generally also go to ‑ier, as in cagey > cagier, choosey > choosier, dicey > dicier, nosey > nosier, pricey > pricier. One-syllable ones, however, do not: fey > feyer, grey > greyer.

  • see english.stackexchange.com/a/68870/19046
    – Alex B.
    Commented Sep 8, 2012 at 15:32
  • 2
    You'll probably find that e.g "grislier", "sillier" are pretty universally accepted. No reason to brand them as being "wrong" as far as I can see. Commented Sep 8, 2012 at 16:20
  • @NeilCoffey I used a question mark because I said I wasn’t sure. I think you are right with the “━ly” adjectives; also add to that chilly, frilly. Oddly, I don’t think you would do the same with an adverb like shrilly, and I can’t see why.
    – tchrist
    Commented Sep 8, 2012 at 16:26
  • This is an excellent, thorough, most informative answer, a better answer than my question deserved. The answer merits an acceptance checkmark from me and a +2; except that, by Stackexchange's rules, I haven't got a second checkmark to give. Accept the +1 and my thanks.
    – thb
    Commented Sep 11, 2012 at 14:25

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