Difference between 到, 到了, and了 to indicate completed action?

Question

It seems 到, 到了, 了 can all be used to indicate completed actions.

What's the difference in terms of indicating an action has finished?

For instance, this grammar page offers a number of examples:

你想到了什么好办法 ？
Nǐ xiǎngdào le shénme hǎo bànfǎ?
Have you thought of any good methods yet?


我们今天学了很多生词 。
Wǒmen jīntiān xué le hěn duō shēngcí.
Today we learned many new words.

In the first example, does the meaning change if you say 想到 instead of 想到了? What if you say 想了?

In the second example, does the meaning change if you say 学到了 instead of 学了? How about 学到?

Answer 1

• 想 is the verb

• 到 is the result complement in 想到 ('think and successfully recall'/ 'think and successfully come up with')

• 想到 does not indicate what tense the action is in. E.g. 將會想到 (future tense); 此时想到(present tense); 曾想到 (past perfect tense)

• 了 indicates 'completed' action (but not an indicator of past tense)

想到 indicates a successful action (you think and come up with something)

想了 indicates a completed action (you thought but might not had came up with anything)

想到了 indicates an successful and completed action (you thought and recalled or came up with something)

Answer 2

了does not mean "completed action", it's a realis aspect marker. Only 到, which is a resultive verb complement, marks the verb as "action reached its goal".

• 你想到了什么好办法 ？ - Have you come up with any good methods yet?
• 你想了什么好办法 ？ - Have you given it a thought?
• 你想什么好办法 ？ - Without 到 complement and withiout 了, the reading should be "habitual" in most cases. That is: You usually think about the good methods?
• 你想到什么好办法 ？ - Still habitual or irrealis/probabilistic reading without 了. That is, You usually come up with good methods?

Answer 3

Regarding 学 and 学到:

• 学 means to study. 我们学了很多生词 indicates you studied lots of new words.
• 学到 means to study + success. It emphasises that something has been learned successfully. 我们学到了很多生词 indicates you LEARNED lots of words