At first glance も appears to be quite a simple particle to use. Its most basic use is to create the meaning of “also” by taking the position of the topic particle as in the below example sentences.
山口さんは 学生です。
田中さんも 学生です。
Yamaguchi-san is a student. Tanaka-san is also a student.
先生は 図書館に 行きました。
山田さんも 図書館に 行きました。
The teacher went to the library. Yamada-san also went to the library.
However, it is important to note that the topic particle has not been made redundant—it is being implied from the context and thus doesn’t need to be shown.
小林さんは 小林さんも 水を 飲みました。
As for Kobayashi-san, Kobayashi-san also drank water.
In other words, it does not replace the topic particle grammatically. This becomes more obvious when we use も in place of the object particle.
川村さんは 魚を 食べました。
川村さんは 野菜も 食べました。
Kawamura-san ate fish. He also ate vegetables.
Here Kawamura-san remains as the topic sentence (and thus would not need to be repeated).
川村さんは 魚を 食べました。
野菜も 食べました。
Kawamura-san ate fish. He also ate vegetables.
You may have noticed that in the above example sentence the inclusive particle も replaces the object particle を. This an except to the general rule for the も particle. As we shall see below, when used with で, に, と it is appended to the original particle.
In fact, you may see をも used in combination but this is extremely rare practice and certainly never used in conversation—formal or otherwise.
亮さんは 学校に 行きました。
映画館 にも 行きました。
Kawamura-san ate fish. He also ate vegetables.
美紀子は 友達と 話しました。
お母さんとも 話しました。
Mikiko spoke to her friend. She also spoke to her mother.
私は カフェで コーヒーを 飲みました。
オフィスでも 飲みました。
I drank coffee in the café. I also drank coffee at the office.
The Position of も
It’s worth just taking a moment to think about the following two sentences:
マイクも 水を 飲みました。
Mike also drank water.
マイクは 水も 飲みました。
Mike also drank water.
They both translate as the same in English but the meaning in Japanese is subtlety different: the former implies that someone else also drank water other than Mike; the latter that Mike drank something as well as water. In English the true meaning of the sentence would only be clear from the context or the preceding statement.