Lesson 5.9 When Something Is Happening

I was just looking for a little bit of a clarification, as some of the flash cards at the end of the lesson brought up a few questions.  I understand that you can て　あります and て　います along with a Transitive and Intransitive verb respectively to show a change in state.

While doing the tests at the end an example would prompt something along the lines of “The lights turned on." which to me seems like a clear change in state.  There is no evidence of human intervention, so I should use the Intransitive 付く and use the て　います to show the change in state. My answer would have been

電気　が　付いて　います。

However in many cases it seems like they were looking for the polite past tense of the verb.

電気　が　付きました。

I felt like for many of the questions at the end of the lesson I found myself saying “The answer is X, or Y” and I was wondering if both are correct ways of interpreting the information given, and when one is appropriate and not the other.

Thank you very much for your patience and understanding.

こんにちは (Konnichiwa) JohnH197,

Thanks for your question. This is a tricky one to explain! 

Transitive & intransitive verbs express a change of state. 

Since “the light turned on” is in the PAST tense, we need to express the change of state in the PAST.

So, we would use the past tense of the intransitive verb 付きます (tsukimasu): 付きました (tsukimashita).

電気が付きました。 (Denki ga tsukimashita.) “The light turned on.”

〜ています (~Te imasu) is the Japanese equivalent of the present continuous ("-ing") form in English (e.g “eating,” “sleeping"). It expresses a CONTINUOUS state - NOT a change in state. 

If we were to attach 〜ています (~te imasu) to 付きます (tsukimasu), we would be using the present tense instead of the past, and be saying “the light IS on” instead of “the light TURNED on”: 

電気が付いています。 (Denki ga tsuite imasu.) “The lights are on.”

To sum things up, whether you need to use 電気が付いています (denki ga tsuite imasu) or 電気が付きました (denki ga tsukimashita) will depend on the English tense used on the flash card. 

If the flash card is in the present tense (i.e "the lights are on"), then you should use 電気が付いています (denki ga tsuite imasu). However, if the flash card is in the past tense, (i.e. “the light turned on”), then you should use 電気が付きました (denki ga tsukimashita).

On a side note, if the flashcard is in the future tense (i.e. “the light will turn on"), then you will need to use the future tense: 電気が付きます (denki ga tsukimasu).

I hope this helped!
Please let me know if you have any other questions.

勉強を頑張ってください！ (Benkyō o ganbatte kudasai!)