Difference between 連用形＋さえ and テ形＋さえ


宿題をやりさえすればいい

宿題をやってさえいたらいい

What is the difference/nuance between these two ways to use さえ with verbs?




>   * 宿題をやりさえすれば
>   * 宿題をやってさえいたら
>

These are both complicated with さえ (="only"), [whose grammar rule may be
difficult](http://maggiesensei.com/2015/03/28/how-to-
use-%E3%81%95%E3%81%88sae/), but after removing さえ, these sentences are:

>   * 宿題をやれば = If you (will) do your homework ...
>   * 宿題をやっていたら = If you have done/finished your homework ...
>

The essential difference is that only the latter has a subsidiary verb
**～ている** , which describes "the continuation of a state" in this case. See
this question for the basics for ～ている: [When is Vている the continuation of
action and when is it the continuation of
state?](https://japanese.stackexchange.com/q/3122/5010)

Compare the following two sentences:

>   1. 明日の昼に宿題をやりさえすればいい。
>   2. 明日の昼(まで)に宿題をやってさえいたらいい。
>

Sentence 1 rather simply refers to your future action. It means you have to do
your homework tomorrow at noon. Sentence 2 means you have to finish your
homework by noon tomorrow; you have to do your homework tonight or tomorrow
morning.

