How do we spell the Present Continuous Tense?

We make the Present Continuous tense by adding -ing to the base verb. Normally it's simple: we just add -ing. But sometimes we have to change the word a little. Perhaps we double the last letter, or we drop a letter. Here are the rules to help you know how to spell the Present Continuous tense.

Basic rule Just add -ing to the base verb:
work working
play playing
assist assisting
see seeing
be being
Exception If the base verb ends in consonant + stressed vowel + consonant, double the last letter:
s t o p
  consonant stressed
vowels = a, e, i, o, u
stop stopping
run running
begin beginning
Note that this exception does not apply when the last syllable of the base verb is not stressed:
open opening
Exception If the base verb ends in ie, change the ie to y:
lie lying
die dying
Exception If the base verb ends in vowel + consonant + e, omit the e:
come coming
mistake mistaking