What is the difference between 以为，认为，觉得， and 想？

以为: I thought this is the case but it's not
认为: I think this is the case, in my opinion
觉得: I feel
想: think/ thinking, want to (but not a must)

eg: 我以为我是对的但是原来她才是对的。
Wǒ yǐwéi wǒ shì duì de dànshì yuánlái tā cái shì duì de.
eng: I thought I was correct but in the end she was correct.

eg: 我认为这个人很坏。
Wǒ rènwéi zhège rén hěn huài.
eng: I think/in my opinion this person is really bad

eg: 我觉得饿了。
Wǒ juédé èle.
eng: I feel hungry

eg: 让我想一下。
Ràng wǒ xiǎng yīxià
eng: let me think a bit
eg: 我想睡觉。
Wǒ xiǎng shuìjiào
eng: I want to sleep.

我认为 我觉得 都是表示你的观点。

我以为，是我主观觉得
以为的内容不一定是对的。

All of these words can mean "think", but they use in different situation.
1. 觉得 in English more means "feel like", so when you say 觉得, it is more of your feeling or sometimes without much thinking and inferring;
2. 认为 is to express your opinion about one thing, e.g. 我认为这则新闻是假的。I 认为(think) the news is fake.(You just show your opinion, but we can not conclude your thinking is right or wrong )；
3. 以为 also has "think" meaning, but when we use 以为, usually the truth is different from our opinion, e.g. you think the girl is ten years old, but actually she has been fifiteen, this "think" you can use 以为；
3. 想 has several meaning:
(1) want to, e.g. 我想回家。I 想(want to) go home; 我想喝水 I 想(want to) drink.
(2)similar to 'guess‘ e.g. 有人来了，我想是他来了。Some one is coming, I 想(guess) it's him.
(3)think or deep think: 让我想想。Let me think.
(4)imagine: 想象

以为, 认为, 觉得, and 想 are all Chinese verbs that express the idea of thinking or having an opinion. While they are similar, there are subtle differences between them in terms of usage and meaning.

1, 以为 (yǐwéi) - to mistakenly think, assume, or believe.
This verb is often used to express that someone thought something was true but later found out they were wrong. It implies that there was a misunderstanding or a mistaken belief.

Example:
我以为他会来，结果他没来。
Wǒ yǐwéi tā huì lái, jiéguǒ tā méi lái.
I thought he would come, but he didn't.

2, 认为 (rènwéi) - to believe, consider, or think.
This verb is used to express one's belief or opinion about something, often based on evidence or reasoning.

Example:
我认为这个计划不可行。
Wǒ rènwéi zhège jìhuà bù kěxíng.
I believe this plan is not feasible.

3, 觉得 (juéde) - to feel, think, or believe.
This verb is used to express one's subjective feeling or opinion about something, often based on personal experience or intuition.

Example:
我觉得这个电影很有趣。
Wǒ juéde zhège diànyǐng hěn yǒuqù.
I think this movie is very interesting.

4, 想 (xiǎng) - to think, want, or intend.
This verb is used to express one's thoughts or desires about something, often in the context of making plans or decisions.

Example:
我想去旅游。
Wǒ xiǎng qù lǚyóu.
I want to go on a trip.

In summary, 以为 implies a mistaken belief, 认为 is used for expressing belief or opinion based on evidence or reasoning, 觉得 is used for expressing subjective feelings or opinions, and 想 is used for expressing thoughts or desires about something.