Adding ED and ING to Verbs

http://www.oxforddictionaries.com/us/words/verb-tenses-adding-ed-and-ing


The past tense refers to things that happened in the past. To make the past tense of regular verbs, the ending -ed is added to the infinitive ('I asked her a question'). The present participle refers to things that are still happening. To make the present participle, the ending -ing is added to the infinitive ('I am asking her a question').
Often there's no need to make any other spelling changes when you add -ed and -ing to the infinitive but there are some cases when it's necessary to do so. Here are some rules to help you get it right:

Verbs ending with a silent e

If the verb ends with an e that isn’t pronounced (as in bake or smile), then you need to drop this final -e before adding -ed and -ing:

verb	past tense	present participle
bake	baked	baking
smile	smiled	smiling

Verbs ending in -ee, -ye, and -oe (such as free, dye, and tiptoe) do not drop the final -e when adding -ing:

verb	past tense	present participle
free	freed	freeing
dye	dyed	dyeing
tiptoe	tiptoed	tiptoeing

A very few verbs keep the final -e when adding -ing to distinguish them from similar words. For example, singe becomes singeing rather than singing (which is the present participle of sing).

Verbs ending with a vowel plus -l

If the verb ends with a vowel plus -l (as in travel or equal), then you need to double the l before adding -ed and -ing in British English:

verb	past tense	present participle
travel	travelled	travelling
distil	distilled	distilling
equal	equalled	equalling

This rule doesn’t apply in American English: see more information about the differences between British and American spelling

Verbs ending with a single vowel plus a consonant

If the verb ends with a single vowel plus a consonant, and the stress is at the end of the word (e.g. refer), then you need to double the final consonant before adding -ed and –ing:

verb	past tense	present participle
admit	admitted	admitting
commit	committed	committing
refer	referred	referring

If the verb ends with a vowel plus a consonant and the stress is not at the end of the word, you don’t need to double the final consonant when adding -ed and -ing:

verb	past tense	present participle
inherit	inherited	inheriting
target	targeted	targeting
visit	visited	visiting

If the verb has only one syllable and ends with a single vowel plus a consonant (e.g. stop), then you need to double the final consonant before adding -ed and -ing:

verb	past tense	present participle
stop	stopped	stopping
tap	tapped	tapping
sob	sobbed	sobbing

Verbs ending with two vowels plus a consonant

If the verb ends with two vowels plus a consonant, you should generally not double the final consonant:

verb	past tense	present participle
treat	treated	treating
wheel	wheeled	wheeling
pour	poured	pouring

Verbs ending in -c

If the verb ends in -c (e.g. panic), you need to add a -k before adding -ed and -ing, and also -er.

verb	past tense	present participle	related noun
picnic	picnicked	picnicking	picnicker
mimic	mimicked	mimicking	mimicker
traffic	trafficked	trafficking	trafficker