The basic form of a verb is called the infinitive. It normally occurs with the word to as in ‘I want to ask you a question.’ Verbs may change their spelling according to which tense is being used.
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:
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 ofsing).
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 lbefore adding -ed and -ing in British English: