Also / only
Particles that widen (mo) or fence off (dake, shika, bakkari) whatever comes before them.
mo
too; also; as many as
も
Takes the place of wa, ga or o to mean 'too / also'. After a number it stresses 'as many as' (mittsu mo tabeta).
watashi mo ikitai
I want to go too.
私も行きたい
watashi mo ikitai desu
I'd like to go too.
私も行きたいです
mo replaces wa, ga and o (watashi mo, never watashi wa mo) but follows other particles (nihon ni mo, tomodachi to mo). A mo B mo = both A and B; with a negative, neither. In casual speech men usually say ore mo or boku mo.
dake
only; just
だけ
Means 'only / just' after a noun, number or clause (sore dake, chotto dake). Any verb can follow, positive or negative.
kyou wa geemu dake shite owatta
Today was just games, and that was it.
今日はゲームだけして終わった
kyou wa geemu dake shite owarimashita
Today was just games, and that was it.
今日はゲームだけして終わりました
'Kore dake?' (just this?) and 'chotto dake' (just a little) are everyday chunks.
shika
only (+ negative)
しか
Means 'nothing but / only' and must be followed by a negative verb. It sounds emphatic or regretful: 'and that's all'.
kyou geemu shika shinakatta
All I did today was play games.
今日ゲームしかしなかった
kyou wa geemu shika shimasen deshita
All I did today was play games.
今日はゲームしかしませんでした
Trap: shika with a positive verb is wrong. Say hitotsu shika nai, never hitotsu shika aru.
bakkari
polite bakarinothing but; only
ばっかり ばかり
Means 'nothing but', with a sense of too much or too often. It is the complaining 'only' (geemu bakkari).
kyou geemu bakkari shiteta
I did nothing but game all day.
今日ゲームばっかりしてた
kyou wa geemu bakari shitemashita
I spent all day just playing games.
今日はゲームばかりしてました
It carries judgement, so use dake for a neutral 'only'. bakka is the clipped casual form you'll hear constantly (geemu bakka shiteru). -te bakari and -ta bakari belong to I.