Patterns of consonant doubling

A tricky aspect of English spelling is the question of doubling consonants when words are suffixed. It’s often cited as an example of UK vs US spelling differences – travel, for example, generates traveller and travelling in the UK, traveler and traveling in the US. But many such words are styled the same in both dialects. So what patterns lie behind this?

Fluent speakers of English have a feel for the rules – some of them anyway – even if they’ve never thought about them. They know that nod forms nodded and red redder (doubling the d), yet brood forms brooded and dead deader (no doubling). Turning flop into an adjective by adding the suffix -y gives us floppy, doubling the p, but soap becomes soapy, with no doubling.

Vowels play an important role. Notice the short vowel in nod and flop and the relatively long ones in brood and soap. Short vowels tend to mean we double the final consonant; long vowels tend to mean we don’t. The latter are often detectable by the word’s ending with e after a consonant: compare mop (mopped) and mope (moped), tap (tapped) and tape (taped), pin (pinned) and pine (pined), and similar pairs.

These generalizations apply to many different word types and suffixes. Final consonants after short vowels are generally doubled (cad → caddish, fun → funny, dim → dimmer), but not after longer vowels (seed → seeded, mood → moody, snoot → snooty), diphthongs (near → neared, maim → maiming), or another consonant (damp → dampen, print → printer, musk → musky).

With longer words, the same guidelines often hold. A single short vowel doubles the consonant (formatting, nutmegged, beginner), a long vowel doesn’t (renovating, inspired). But syllable stress also comes into play – compare offered and referred, enveloped and equipped, budgeting and upsetting. A stressed last syllable tends to require consonant doubling (so long as the vowel is short), while an unstressed last syllable doesn’t.

This being English, there are other exceptions. L is something of a law unto itself, often doubled regardless of stress (compelling, labelling, marvelled, yodelling) – especially in British English, less so in American English. There are exceptions to this exception (paralleled in both British English and American English), there are consonants not predictably covered by these generalizations (h, j, q, w, x and y), and there is no shortage of grey areas (focus, combat).

The best rule is to use your dictionary. Even native speakers of English usually have a few words they check regularly for this reason. Just below each headword, Macmillan Dictionary has a ‘Word Forms’ button; clicking it produces a box showing how the word is inflected. And at the bottom of each definition is a link from British English to American English and vice versa. These features are well worth exploring if the area gives you difficulty.