"I did not study yesterday."
-ませんでした is the polite past ending. Since the original is in the past tense, you have to use the past tense here as well.
-しませんis for present negative while -しませんでした is used for past negative
Adding でした (or just changing the す to した for positive verbs) changes the ますform of the verb to past tense.
About adding or not the は after 今日, 明日 etc, somebody please tell me if this is correct? I feel like it depends on the question/sentence that led to the one we're translating, for example: If someone asked "what did you do yesterday?" we would add the は because "yesterday" is the topic. If they asked "when did you study?" we would not add the は because "studying" is the topic. So both answers should be accepted because we don't have this context to base our answer on. How far from right is this?
The similar sentence "I did not work the day before yesterday" used the 'so'/'wo' particle after the verb, before "shimasen deshita". What's with that difference? Is it a tone/meaning thing or do some verbs just not need it?
It is because べんきょうします is a verb in itself, while しごと is a noun, that you have "to do", therefore the particle を before the verb します. The verb for work is はたらく.
I still don't understand this. べんきよう is a noun, just like しごと (to my knowldege). So why is the particle を needed after one and not the other when using them as verbs?
べんきょう is a noun, the act of studying, so it needs します to turn into a verb. べんきょうします would be something close to "the act of studying"
So..... Am i not able to leave the time without an attached particle. 昨日勉強しませんでした。i thought i could say that
When i was taking japanese classes we never once used は in this context and it is odd for me to do it. Doubly so when the particle after times/dates is usually に i.e. you would say 8月７日にきました (i came on aug. 7) or 9時に起きました (i woke up at 9)
Using the を is also technically correct. べんきょうします (benkyoushimasu) is somewhat special in that it doesn't need an を though. べんきょうをします would basically be like saying, "I do studying." It's not wrong, but it's unnecessary when you could just say "studying" to mean the same thing.
For example, if someone asked what you were doing tonight, you'd normally just answer, "I will be studying," not "I will be doing studying."
Because of the negation. There is no negative past tense form for "shimasu", so the verb is negated normally by adding "-en" and the past tense form of "desu" is added. Therefore, "shimashita" is negated as "shimasen deshita". The English comparison would be that "I studied" would be negated as "I didn't study" rather than "I studiedn't".
I'm a little confused when to use ました and でした. Any pointers or a simple explanation will do