Is there any rhyme or reason to when one should double the last consonant when adding -ed or -ing? [duplicate]

Possible Duplicate:
focussed or focused? The double consonant

Sometimes, final consonants are doubled when adding -ed or -ing to the end of a verb whose penultimate letter is a vowel.

• stop → stopping
• grab → grabbing
• mar → marring
• run → running

But sometimes, the consonant is not doubled.

• label → labeling
• madden → maddening
• book → booking

Is there any way to tell whether it will be necessary to double the letter in a generic way, or is this another case of English's general rule of "you must memorize all cases separately"?

I think this also relates to pluralizing nouns in some cases, although an example escapes me at the moment.

Solution 1:

I am not certain of the underlying linguistic rule, but there is a loose English pronunciation rule, explicitly taught in schools to help remember spellings, that says certain vowels that are separated from 'e' or 'i' by only a single consonant will change their pronunciation. When the original pronunciation of the vowel must be maintained, the consonant doubles to put the following vowel far enough away to not trigger this rule.

Note that 'e' as a first vowel is immune to this change, as is the 'oo' in "book". (And note that "label" can be spelled either "labelled" or "labeled", depending on local standards, but this is not a matter of pronunciation and is a purely orthographic issue.)

So:

• stop → stopping (pron: "stahping")
• *stop → stoping (pron: "stohping", the removal of ore from a mine)

• grab → grabbing (pron: "grahbing")
• *grab → grabing (pron: "graybing", not a word)

• mar → marring (pron: "mahring")
• *mar → maring (pron: "mayring", which perhaps has to do with female horses)

• run → running (pron: "ruhning")
• *run → runing (pron: "rooning", which might be "to inscribe with runes")

(Where the * indicates a transformation that a native speaker would judge "wrong".)

The complementary transformation can be seen when the original word is already structured with a 'e' or 'i' following a vowel with a single consonant between. Since the pronunciation of the first vowel is already altered by the second vowel, the consonant does not get doubled in the gerund form:

• rake → raking (pron: "rayking")
• pale → paling (pron: "payling")

Solution 2:

In at least some cases, using a single consonent could indicate that the vowel had a hard sound - like if the word ended in an e - whereas the double consonant indicates that it's a soft sound. This is particularly true considering that a word that ends in e is likely to lose the e when its turned into a gerand (and ends in ing).

For instance, rake becomes raking. If it had become rakking, then the a would have had a soft sound instead of a hard one, thereby changing the pronunciation.

So, generally-speaking, the fact that it's a double consonant instead of a single consonant indicates that the vowel is soft. Now, English being English, such a rule is not applied 100% consistently, but in the three examples that you gave, you can see that the double consonant isn't needed.

Having a single l in labeling would not imply a hard e any more than it would in label. Having a double b, however, would indicate a soft a, so there's only one. The same goes for maddening. You wouldn't have a hard e would only one n, so the double n is not necessary. However, because a is soft, you have two d's rather than one. In the case of booking, there is no hard and soft oo sound, so only the one k is required.

So, the general rule has to do with making sure that the vowel preceding the double consonant is soft. So, in words where the vowel is hard or it's not the first vowel and is soft regardless, only a single consonant is required.