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 or form is being used.
Past and -ed forms
The past and -ed forms are the same in regular verbs. The following are the spelling rules for regular verbs.
We add -ed to the base form of the verb:
clean → cleaned echo → echoed email → emailed sail → sailed
If the word ends in -e, we add -d to the base form of the verb:
agree → agreed dine → dined love → loved
If the word ends in a consonant + -y, we change the -y to i before -ed:
apply → applied cry → cried
There are three common exceptions, where we change the -y to i after a vowel and just -d is added:
pay → paid say → said
-ing forms
The general rule is add -ing to the base form of the verb:
go → going hurry → hurrying play → playing
If the word ends in -e, we drop the -e before -ing:
love → loving lose → losing write → writing
But if the word ends in -ee, -ye, or -oe, we keep the -e:
agree → agreeing dye → dyeing (compare: die/dying) see → seeing
If the word ends in -ie, we change the -i to -y and we drop the -e before -ing:
die → dying lie → lying tie → tying