If there are multiple helping verbs, then the last helping verb determines the form of the main verb
"to finish"
They should finish soon.
They should have finished soon.


Regular and Irregular Verbs

Forms of Verbs

Base Present Past Past Participle -ing Form
ask ask ask(s) asked asked asking

When to use the forms
--"to+verb"
I want 'to go' to Asia World.

Base: Use after "can, may, shall, will, could, might, should, would, must, do, does"
--You can play piano if you pay money for lessons.
--I could ask him to come to my office.
--I can see clearly.
--I may travel to America later this week.
--I shall yell at the sleeping student.
--I will study more.
--I could study more, but I won't.
--I might go to the movie next week.
--I should take out the trash.
--I would like to buy a CD for my boyfriend.
--I must study harder.
--I do like to listen to music.
--He does think about our relationship.
--He did ask me to go with him to the concert last week.

Present
I ask, you ask, he asks, we ask, you all ask, they ask
--He plays soccer every day.

Past
asked
--He played soccer for many years.
I asked, you asked, he asked, we asked, you all asked, they asked

Past Participle: Use after "have, has, had"; some are used after forms of "be."
--I have gone shopping....
--She had played piano well when she still had her hands.
asked
--I have asked him for help before, but he always has said, "No."
habitual (regular) action set in the past

-- -ing form
Use after forms of "to be"
--He is going to eat lunch after class.
--Her husband is playing for her.
--I am asking you nicely to stop beating [noun] me up.

--Common Irregular Verbs--
be
become
begin
break
bring
buy
build
catch
choose
come
do
draw
drink
drive
eat
fall
feel
fight
find
forget
forgive
freeze
get
give
go
grow
have
hear
hold
keep
know
lay (to put) laid
lead led
leave
lie (to rest) lay lain lying
lose
make
meet
pay
read
ride ridden
ring
rise
run
say
see
sell
shake shaken
shine (give light) shone
shine (polish) shined
sing
sleep
speak
spend
stand
steal
strike
swin swum
swing swung
take
teach
tear tore torn --I had torn up all of his letters.
tell
think
throw
wea wornr
win
write