summer

1. What is the difference between these two?

в то лето

and

летом

2. Also, why wouldn't the first one be in the prepositional case as "в том лете" ?

3. How would you say "on that day" ?

When you say "летом" you mean recent summer. But what if you want to speak about some other summer, for example 5 years ago? In certain cases it may be not clear whether you meat that summer or recent summer, so mentioning explicitly "that summer" may be handy.

2. If you say "В том лете" in prepositional case, you mean that something was literally in, inside the summer. In some weird cases you can use prepositional case, i.e "В том лете было маловато лета" (There were little summer in that summer), but in most cases prepositional case is a no-go.

3. "В тот день". Accusative case again. On other hand "в том месяце" и "на той неделе" are in prepositional case. Have no good explanation for it.

Выражения в том лете или в той зиме, весне, осени мне как-то никогда не попадались. Обычно говорят тем летом, той весной, зимой, осенью.

Quote:

---

Originally Posted by Suobig

В том лете

---

Sounds so wrong.

1. В то лето = That summer, i.e. summer of a particular year (BC, AD, doesnt matter, a particular year will be meant)
Летом = in the summer, summertime - Year is not important, season is specified.

2. в том лете - grammatically incorrect. The rule of declension and preposition use dictate в то лето. A simpler form is Тем летом (=That summer), which is very often used.

1. в + accusative:

RIGHT: в ту секунду. WRONG: в той секунде, той секундой.
RIGHT: в ту минуту. WRONG: в той минуте, той минутой.
RIGHT: в тот час. WRONG: в том часе. (тем часом is OK, but means "while", "whereas")
RIGHT: в тот день. WRONG: в том дне, тем днём.
RIGHT: в тот понедельник/вторник/четверг/воскресенье
RIGHT: в ту среду/пятницу/субботу

2. в + prepositional OR в + accusative
RIGHT: в том месяце. BOOKISH: в тот месяц. WRONG: тем месяцем.
RIGHT: в том сезоне. BOOKISH: в тот сезон. WRONG: тем сезоном.
RIGHT: в том году. BOOKISH: в тот год. WRONG: тем годом.
RIGHT: в том десятилетии. BOOKISH: в то десятилетие. WRONG: тем десятилетием.
RIGHT: в том веке. BOOKISH: в тот век. WRONG: тем веком.
In these phrases, в том + Prepositional Case has several meanings: "that X" (i.e. "given", "mentioned") or "the last X / the past X" or (rarely) "the next X".
В тот + Accusative Case has the first meaning only.

Please, note, that неделя used with the preposition на, not в:
на той неделе

3. instumental OR в + accusative:
RIGHT: тем летом, в то лето. WRONG: в том лете.
RIGHT: той осенью, в ту осень. WRONG: в той осени.
RIGHT: той зимой, в ту зиму. WRONG: в той зиме.
RIGHT: той весной, в ту весну. WRONG: в той весне.

Again, тем/той + Instumental Case can mean "that", "the last" or "the next", depending on context, and в то/ту + Accusative Case means "that" only.