Rules for forming the past tense

1) Past-tense forms of verbs are either regular or irregular. Generally, add -ed to the base form; for verbs ending in a silent -e, add -d; for verbs ending in a consonant + y, change -y to -i and add -ed
2) For stressed closed-syllable verbs ending in one vowel + one consonant, double the final consonant; otherwise just add -ed
preFER->preFERRed
VISit->VISited
3) If the verb does not end in one vowel + one consonant, add -ed
start->started (ends in two consonants)
need->needed
4) One vowel + y: add -ed
stay->stayed