existed,一般过去式动词构词规则？
不知道你现在读几年级，所以没办法给出精准的建议existed。
如果你是小学生，只需记住be，do, have, go等常用词的过去式就行了，没有必要学得那么复杂，多了你也记不住。
如果你是中学生，那么，下面这些，或许对你有帮助。
1.规则动词的过去式(1).通常在原动词后加”ed”
listen-listened
look-looked
wash-washed
brush-brushed
paint-painted
call-called
climb-climbed
jump-jumped
shout-shouted
work-worked
talk-talked
open-opened
answer-answered
(2).如果原动词以“e”结尾，直接在词尾加”d”
like-liked
live-lived
close-closed
raise-raised
love-loved
taste-tasted
move-moved
hope-hoped
exercise-exercised
practice-practiced
(3).如果原动词以辅音字母加”y”结尾，通常将“y”变为“i”再加“ed”
cry-cried
carry-carried
marry-married
bury-buried
worry-worried
hurry-hurried
try-tried
study-studied
copy-copied
justify-justified
embody-embodied
(4)如果原动词是以重读闭音节结尾，则需双写尾字母，再加“ed”
stop-stopped
drop-dropped
drip-dripped
cup-cupped
beg-begged
drag-dragged
dot-dotted
plan-planned
2.不规则动词的过去式(1).元音字母“i”变为“a”
swim-swam
drink-drank
sink-sank
ring-rang
sing-sang
give-gave
sit-sat
spit-spat
begin-began
(2).元音字母“i”变为“o”
drive-drove
rise-rose
ride-rode
shine-shone
win-won
write-wrote
(3).元音字母“ea/a”变为“o/oo”
speak-spoke
take-took
shake-shook
wake-woke
(4).将字母组合“ow/aw”变为“ew”
blow-blew
know-knew
grow-grew
draw-drew
(4).将字母组合“eep”变为“ept”
sleep-slept
keep-kept
sweep-swept
(5).将字母组合“ay”变为“aid”
lay-laid
pay-paid
say-said
(6).将尾字母“d”变为“t”
spend-spent
build-built
lend-lent
其余的，就要靠自己去归纳、总结和整理了！
要学好过去式，仅仅背诵词的时态变化是不够的。你要去运用！就是自己用过去式来写句子或者短文。要会用，首先就要知道在描述事物时，什么情况下要用过去式。下面也为你归纳整理出来，自己有时间，认真看一下。
3.动词过去式的用法(1).表示过去某时间发生且已结束的动作
He saw Mr. Smith yesterday. (他昨天看见了史密斯先生。)
They worked in the factory in 2017.（2017年，他们在那家工厂工作。）
Jack played football with his friends yesterday.（杰克昨天与朋友们一起踢足球。）
(2).表示在过去存在或持续了一段时间的某种状态
Qin Dynasty existed for only fifteen years. （秦朝享国仅为15年。）
We lived in Boston in nineties. (九十年代我们住在波士顿。)
They were close friends in their lifetime. (在世时，他们是好朋友。)
(3).表示过去经常发生的动作或多次反复的行为
Paul went to school by bike when he was a child. (小时候，保罗骑自行车上学。)
He always took a walk along Wei Ming Lake every morning when he studied in Beijing University.(他在北大学习期间每天早上都沿着未名湖散步。)
David applied for a visit to France for 6 times before he got one. (戴维想到法国看一看，申请了6次才获批准。)
(4).谈论过去的事情，主句用过去时，从句也用过去式，尽管从句所说的情况现在依然存在。这是为了保证时态一致。
Jack got the job because he was a good reporter. (杰克得到那工作是因为他是一名好记者.)(现在还是好记者)
I found the twins looked alike. (我发现这两个双胞胎长得好像。) （两人现在还是长得好像。）
Mary said that her mother was Italian. (玛丽说她妈妈是意大利人。)（她妈妈现在仍然是意大利人）
(5). 用于对已去世的人的情况描述
Hua Tuo was a great doctor. (华佗是一名伟大的医学家。)
Washington was the founder of the USA.(华盛顿是美国的奠基人。)
The First Emperor of Qin united China. (秦始皇统一了中国。)
如果你是高中生，还需掌握下面的用法：
(6).在虚拟语气中，用过去表示现在
It’s time you had a holiday.(你该度假了。)
I wish you lived closer to us.(我希望你住得离我们近点！)
I’d rather you did it now.(我到宁愿你现在就去做！)
(7).过去时与ever, never, once连用，表示过去的经验
Did you ever see a lion? (你见过狮子吗？)
I never saw such a beautiful city before. （我从未看见过这么美丽的城市。）
They once experienced a tsunami in Japan.(他们曾在日本经历过一次海啸。)
如果你是大一在读，下面的用法也应了解
(8).代替过去完成时，说话人不强调先后与因果关系
She apologized/She was sorry for what she said.(她说她为自己所说的一切道歉。)
Did you find the pen you lost?（你找到你丢了的笔了吗？）
We all went to bed when the clock struck ten.(钟敲十点的时候，我们就睡觉了。)
供你参考，加油！
