Difference between "believe" 认为 and 相信? This question is related to:
Is there any difference between 想, 觉得 and 以为?
What are the difference between e.g. 想, 觉得 and 认为 when expressing opinion?
In there, they mentioned both 认为 rènwèi and 相信 xiāngxìn mean to believe. I would like to know what differences they have in usage.
The key character in 相信 is 信 which means faith/trust. (相 is just there to turn 信 into a standard two-character word. It can be omitted in spoken language.)  I.e. there's some emotion involved. The object can also be a person or a belief (i.e. equivalent to &quot;believe in&quot;).
For example, 我相信你 means &quot;I trust you&quot;/&quot;I have faith in you/what you said&quot;.
认为... is literally &quot;recognise ... as&quot; and can be roughly translated as &quot;have the opinion that&quot;. It involves no emotion, but a mere statement of thought. Also, it must be followed by a statement clause and not a simple subject.
Compare and contrast
相信 and 认为 are not interchangeable due to context:

我相信未来会更好 （Using 认为 will sound presumptuous)
科学家认为大爆炸是宇宙的起源 (相信 will make the belief sounds less scientific and more wishful thinking)



我相信我儿子是不会做坏事的
警方认为你儿子触犯了法律 (认为 is treated as stating a fact. When used with a character judgement, some kind of authority or evidence is required. Otherwise, it will sound libellous.)

They are not interchangeable due to grammatical structure:

我相信进化论 (= I believe in evolution.)
我认为进化论是真理 (= I believe that evolution is true.)