When do you use は/に for どようびは/に?


There is a sentence in a worksheet that goes: どようびは ほんを よみます。Why is it not
どようびに? When do I know which one to use and what is the difference?

Spoke to my sensei and she said you can use something like: どようびには, which
would still be right ... I didn't quite get what she meant. Can someone please
clarify, thank you.




The main difference is probably the nuance of the sentence.

は is used as emphasis on どようび as the topic of the sentence. "On _Saturdays_ I
will read books." (Only Saturday, and not any other day of the week.) It may
imply that reading books on Thursday is a habit of the speaker.

には is acceptable as well and means the same thing because は already indicates
emphasis on どようび. に helps to clarify that it is when the action takes place,
but it is quite clear even without it that どようび indicates the time of action.

If only に is used, however, it means that "On Saturday I will read books."
(Presumably the coming Saturday.) The action, _to read books_ , and not when
it is done, is emphasized. It does not imply that it is a habit or routine, it
just so happens that the speaker plans to read books on a Saturday.




The main difference is probably the nuance of the sentence.

は is used as emphasis on どようび as the topic of the sentence. "On _Saturdays_ I
will read books." (Only Saturday, and not any other day of the week.) It may
imply that reading books on Thursday is a habit of the speaker.

には is acceptable as well and means the same thing because は already indicates
emphasis on どようび. に helps to clarify that it is when the action takes place,
but it is quite clear even without it that どようび indicates the time of action.

If only に is used, however, it means that "On Saturday I will read books."
(Presumably the coming Saturday.) The action, _to read books_ , and not when
it is done, is emphasized. It does not imply that it is a habit or routine, it
just so happens that the speaker plans to read books on a Saturday.

