Think, feel, mind
Verbs for what's going on in your head: an opinion (omou), thinking it over (kangaeru), something on your mind (ki ni naru), a hunch (ki ga suru), minding it (ki ni suru) and taking care (ki o tsukeru).
omou
polite omoimasuthink (that)
思う おもう 思います
Attaches with to to any clause to state an opinion or guess softly (ii to omou), and -ou to omotteru states a plan.
ashita ame furu to omou.
I think it'll rain tomorrow.
明日雨降ると思う。
ashita ame ga furu to omoimasu.
I think it will rain tomorrow.
明日雨が降ると思います。
Someone else's view uses omotteru (Tanaka-san mo sou omotteru); nouns and na-adjectives keep da before to: ii hito da to omou, kirei da to omou (never *ii hito to omou).
Learn alongside: kangaeru, ki ni naru, ki ga suru, ki ni suru, ki o tsukeru
kangaeru
polite kangaemasuthink over; consider
考える かんがえる 考えます
Actively thinking something through or coming up with ideas, and the polite way to put off a decision (chotto kangaete mimasu / kangaete okimasu).
sore, mada kangaeteru.
I'm still thinking about that.
それ、まだ考えてる。
sore wa mada kangaetemasu.
I'm still thinking that over.
それはまだ考えてます。
Hearing chotto kangaete okimasu usually means a polite no; 'I think that ...' is to omou, not to kangaeru.
Learn alongside: omou, ki ni naru, ki ga suru, ki ni suru, ki o tsukeruLearn first: omou, -teru
ki ni naru
polite ki ni narimasube curious about; bother
気になる きになる 気になります
Something keeps pulling your attention, as curiosity, interest or worry, with the thing marked by ga (X ga ki ni naru).
ashita no tenki, ki ni naru.
I'm a bit worried about tomorrow's weather.
明日の天気、気になる。
ashita no tenki ga ki ni narimasu.
I'm a little concerned about tomorrow's weather.
明日の天気が気になります。
Its active partner: ki ni shinaide = don't worry about it.
Learn alongside: omou, kangaeru, ki ga suru, ki ni suru, ki o tsukeruLearn first: naru
ki ga suru
polite ki ga shimasuhave a feeling (that)
気がする きがする 気がします
Attaches to any clause to mark it as a hunch rather than a claim (... ki ga suru), sounding more intuitive than to omou.
ashita ame furu ki ga suru.
I have a feeling it'll rain tomorrow.
明日雨降る気がする。
ashita ame ga furu ki ga shimasu.
I have a feeling it will rain tomorrow.
明日雨が降る気がします。
No to: a clause attaches directly (furu ki ga suru); a na-adjective takes na and a noun takes mitai na (hen na ki ga suru, uso mitai na ki ga suru).
Learn alongside: omou, kangaeru, ki ni naru, ki ni suru, ki o tsukeruLearn first: suru, omou
ki ni suru
polite ki ni shimasumind; worry about
気にする きにする 気にします
Says someone minds or worries about something, with the thing marked by o; mostly heard as ki ni shinaide (don't worry about it) after an apology or thanks, and ki ni shinai (I don't mind).
ii yo, ki ni shinaide.
It's fine, don't worry about it.
いいよ、気にしないで。
ii desu yo, ki ni shinaide kudasai.
It's fine, don't worry about it.
いいですよ、気にしないでください。
Also mada ki ni shiteru no? = are you still worried about that?
Learn alongside: omou, kangaeru, ki ni naru, ki ga suru, ki o tsukeruLearn first: suru, -naide, ki ni naru
ki o tsukeru
polite ki o tsukemasube careful; take care
気をつける きをつける 気をつけます
Means paying attention so nothing goes wrong; ki o tsukete (take care, get home safe) is a standard goodbye, and ki o tsukemasu (I'll be careful) answers a warning or closes your own apology (sumimasen, kondo kara ki o tsukemasu).
ki o tsukete kaette ne.
Get home safe.
気をつけて帰ってね。
ki o tsukete kaette kudasai ne.
Get home safe.
気をつけて帰ってくださいね。
The danger takes ni: kuruma ni ki o tsukete = watch out for cars.
Learn alongside: omou, kangaeru, ki ni naru, ki ga suru, ki ni suruLearn first: -te