今日はこれで終わります = That's it for today. Why is で used?

Hi all. I'm not sure why で is used here. In fact, I don't know why これで is necessary here at all. Would 今日はおります not suffice? Could someone please explain? Thanks :>

(This is from the 12th chapter of Genki 1, pg. 265 if you're interested).

typo: おわります, not おります

これ refers to the lesson/exercise/explanation the teacher is doing now in the class, and で indicates the end of the range/area. This で can be used both for spacial and temporal.

この質問でインタビューは終わりです。
My interview ends with this question.

明日で夏休みは終わりです。
The summer vacation will be over tomorrow.

GenjiMain said:

で

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GenjiMan,

In this situation, I translate "で" as "within the limits of". So here これで could be translated as "within the limits of today", which is a way of emphasizing that the lesson is ending right here and now. This is similar to the English sentence, "This TV program has been brought to you by Honda Motors," wherein the use of present perfect merely emphasizes the time at which this is happening (as opposed to, "This TV program was brought to you by Honda Motors.")

In addition, adding これで with で as a 'preposition' gives the sentence a clearer meaning, in that it adds a 'prepositional phrase' that is the same as the word 'today' in the sentence "That's it for today". (An important difference here is that the English word 'today' does not take a preposition.)

So, what do you think the function of 今日は is in that sentence? で is attached to これ, not 今日, and これ doesn't refer to 今日 there.

Toritoribe-sensei!

The way I see it, これ refers to either this moment or whatever endeavor is presently in progress. So I see 今日は as referring to "That's it for today."

Yes, that's exactly what I explained. Well, then, I don't understand why you said 'So here これで could be translated as "within the limits of today"' or 'In addition, adding これで with で as a 'preposition' gives the sentence a clearer meaning, in that it adds a 'prepositional phrase' that is the same as the word 'today' in the sentence "That's it for today"'. これ and で both have nothing to do with "today" in that sentence.