Seeing Double-le

Duolingo lately introduced me to the use of the toneless particle 了 le twice in a single sentence.

Of course, I had come across sentences with two occurences of 了 le before, such as

我 吃 了 太多 饺子 了 wǒ chī le tài duō jiǎozi le ("I have eaten too many dumplings")

But the second use of 了 le when combined with 太 tài means "too much of" something, so that doesn't really count. E.g., 太 贵 了！ tài guì le! ("Too expensive!")

The kind of double-le sentence Duolingo meant was something like this:

我 这里 工作 了 十年 了 wǒ zhèlǐ gōngzuò le shí nián le ("I have worked here for 10 years")

Notice that the second part of the sentence 十年 了 shí nián le ("for 10 years") changes the implied tense of the first.

If we had just said,

我 去年 这里 工作 了 wǒ qùnián zhèlǐ gōngzuò le ("I worked here last year")

that would have been the simple past tense. Adding 十年 了 shí nián le ("for 10 years") changes the implied tense of the verb from "I worked" to "I have worked".

Here's a slightly more complex example.

我 等 你 等 了 一个 小时 了 wǒ děng nǐ děng le yīgè xiǎoshí le ("I have been waiting for you for an hour")

The first 了 le qualifies the verb 等 děng ("wait"), while the second 了 le qualifies the time 一个 小时 yīgè xiǎoshí ("one hour"), changing the implied tense from "I waited" to "I have been waiting".

[Aside:

Notice also that the verb 等 děng ("wait") is repeated, which seems to happen with transitive verbs. I had written about this before. To qualify the verb, you first use it along with its object, then repeat the verb alone without the object and suffix it with a 了 le.

我 等 你 等 了 一个 小时 了 wǒ děng nǐ děng le yīgè xiǎoshí le (literally, "I wait you wait (le) one hour (le)")

I suspect that transitive verbs and their objects have a very strong "electrostatic" bond in Chinese, which often renders them as a single word. You never just say 吃 chī ("eat"); you always say 吃饭 chīfàn ("eat rice") or use some other food object as part of the compond verb. Free-floating transitive verbs are like ions. They're never found alone, because their charge strongly attracts and binds them to objects with the opposite charge. You have to explicitly "ionise apart" the two components to be able to qualify the verb alone.

我 跑步 跑 得 很 快 wǒ pǎobù pǎo dé hěn kuài ("I run fast", literally "I run steps run (adverb indicator) (connector) fast"). The two words in 跑步 pǎobù (literally "run steps") always go together and masquerade as a single instransitive verb "to run" -- until you need to qualify it in some way. Then the actual verb 跑 pǎo has to be repeated separately for that purpose.

End aside]