While all of them involve the mind in some way, the English verb “to think” has many shades of meaning. Consider the following sentences:
(1) I think that movie was quite good.
(2) I’m thinking about whether I want to go out to eat tonight.
(3) I’m thinking about what the results will be if I handle it that way.
(4) That argument is very complex, I’m still thinking about whether I agree with it.
(5) I think that’s the right answer.
In (1), the speaker is offering an opinion about the movie. In (2) and (3), he is trying to decide whether to do something. In sentence (4), there’s also an idea of not having decided yet, but here the speaker is really deciding whether or not he agrees with some complex argument, and the thinking process is at a higher, more complicated level then in the other sentences. Finally, in (5) he is expressing probability – it’s more likely than not that the answer offered is the correct one, but he’s not certain.
So how to translate different conceptions of the English verb “to think” into Chinese? I don’t claim to have entirely resolved it, but this is how I, well, think about it.
If “to think” means “to have an opinion about,” the best translation is usually juéde (觉得) or rènwéi (认为).
The meanings of these two words are pretty much the same, the only difference being that 认为 is a little more formal, more likely to be the choice in written usage. But in oral Chinese both are common. So for (1) the question and answer together are
(你觉得)这部电影怎么样？ ((Nǐ juéde) Zhèibù diànyǐng zěnmeyàng?) How do you think that movie was?
(我觉得) 非常好。((Wǒ juéde) Fēicháng hǎo.) (I think it was) really good.
Note that for both question and answer, in both English and Chinese, sentences with no subject and no verb meaning “to think” might be OK depending on the context of the conversation. But if you want to explicitly include “to think,” 觉得 (or 认为) is the best choice here. Either of these verbs might can be used in (5), e.g. 我觉得他的答案是正确的 (Wǒ juéde tā de dá’àn shì zhèngquè de).
Note also that “to think” has some overlap in English with “to feel,” and the latter doesn’t always imply a lack of cogitation, of reasoning. “I though his argument wasn’t good” and “l felt his argument wasn’t good” aren’t much different. Of course, sometimes only “to feel” is correct — “I felt bad for him,” is an emotional statement, and so “I thought for him” would mean something different— “I thought in his place,” or something like that. But a core character for “emotion” in Chinese is 感 (gǎn), and this is generally used for thought that is not substantially rational, and instead more instinctive. 感觉 (gǎnjué) can be “a feeling” or “to feel,” and 感到 (gǎndào) means “to feel” (not in the general sense, like 觉得 or 认为, but in response to some specific event). In English, “Walking home from work I felt the street was crowded” and “Walking home from work I thought the street was crowded” are both the same, although maybe “thought” feels a bit more like you made a reasoned comparison between today and most days. In Chinese, while using one of the two “to have an opinion” words as in 今天走路回家的时候，我觉得人特别多 (Jīntiān zǒulù huíjiā de shíhòu, wǒ juéde rén tèbié duō) is fine, you would seldom use 想. Even 认为, because it lacks the 觉 character, which suggests “to feel” or “to sense,” sounds a little stiff. But if you say 今天走路回家的时候，我感觉到了人特别多 (Jīntiān zǒulù huíjiā de shíhòu, wǒ gǎnjuédào le rén tèbié duō), it unquestionably indicates feeling and not deliberating.
Another common translation for “to think” is the single-character verb 想 (xiǎng).
This character alone means “to think about,” but often seems to me to be used when what you are thinking about is not so substantial. For example, sentence (2) above in Chinese might be:
你在想什么？ (Nǐ zài xǐang shénme?) What are you thinking about?（我在想）今天晚上要不要去餐厅。 ((Wǒ zài xiǎng) Jīntiān wǎnshang yào bú yào qù cāntīng.) (Right now I’m thinking about) Whether I want to go out to eat tonight. Again, the subject and the verb phrase might be optional.
Question (3) can also be answered, 我还在想，如果（我）这样处理（这个问题），后果会怎么样？(Wǒ hái zài xiǎng, rúguǒ (wǒ) zhèyàng chǔlǐ (zhèige wèntí), hòuguǒ huì zěnmeyàng?)
The character 想 is used to form many two-character words involving not pondering some deep matter but nonetheless involving the mind:
想要 (xiǎngyào), “would like to, want to”
想念 (xiǎngniàn), “to miss” (as in a person, place or time)
想到 (xiǎngdào), “to think of” — usually something you already know about, just not on your mind until just this moment, e.g. (我)每(一)次想起我母亲，就想到她的手工蛋糕((Wǒ) Měi (yí) cì xiǎngqǐ wǒ mǔqīn, jìu xiǎngdào tā de shǒugōng dàngāo), “Every time I think of my mother, I think of her homemade cake.”
想起(来)(xiǎngqǐ(lái)) also means “to think of,” but with an emphasis on the suddenness of it — a solution to a problem, a new idea, or suddenly recalling something. I have searched online, and the romantic line “Every time I think of you” is translated both as 我每一次想到你 and 我每一次想起你, although the latter feels more appropriate to me.
Note that Chinese isn’t partial to using the verb for remember, 记得 (jìde), if the context has that suddenness to it. 我记得，我小时候 …… (Wǒ jìde, wǒ xiǎoshíhòu ……) means “I remember when I was a child…” and is fine, as is 我记得，他没有回答” (Wǒ jìde tā méiyǒu huídá), “I remember, he didn’t answer.” But if the meaning is “l remembered I have to stop by the supermarket after work,” don’t use 记得, and instead say 我想起来，下班以后得去超级市场 (Wǒ xiǎngqǐlái, xiàbān yǐhòu děi qù chāojíshìchǎng).
Finally, there are three words I am aware of that both have the deeper meaning of “think about” as “ponder” or “reflect on.”
While English speakers can ironically use these latter two terms even if they are thinking about something trivial (“I pondered long and hard about what to order”), in general these words are used when you were thinking about some deeper matter. The ones I have encountered most frequently are 思考 (sīkǎo), 深思 (shēnsī), and 考虑 (kǎolǜ).
Since 深 (shēn) means “deep,” 深思 is pretty easy — it means “to think deeply about,” more like “ponder” or “reflect on.” (思, sī, also means “to think,” but at a deeper level than 想.) A native-speaker friend of mine gave me this distinction (her words):
“深思: think in depth
思考: think about in general
考虑: consider a proposal”
So whereas the first two don’t need to end in a decision — you can “think about his view of the world” (思考他的世界观, sīkǎo tā de shìjièguān), 考虑 requires that you be thinking about whether to do something — “I’m thinking about whether I want to go to college” (我在考虑要不要念大学, Wǒ zài kǎolǜ yào bú yào niàn dàxué). Or, statement (4) above can be translated as, 这个论点很复杂，我还在思考同不同意 (Zhèige lùndiǎn hěn fùzá, wǒ hái zài sīkǎo tóng bù tóngyì.)
It’s a bit more advanced grammatically, but note that 在 (zài) here means to be in the process of doing something. The way this word is used is interesting in its own right, and might be the subject of a future article.
Finally, “opinion” is commonly translated as 意见 (yìjiàn) or 看法 (kànfǎ). The second translates as ”method of seeing,” and English has pretty much the same wording – “way of looking at it,” “way of seeing it.” These are nouns, just like “opinion.” The character 法 (fǎ) means among other things “method,” and it is pretty widely used. Indeed, 想法 is used somewhat similarly to the English phrase “way of thinking —“The way I thought about it, he was a man, so…” (我的想法是，他是男人，因此……, Wǒ de xiǎngfǎ shì, tā shì nánrén, yīncǐ ……). (You will have to complete that sentence yourself.) The many ways 法 can be used is also a topic for another time.