When combined, 相 (xiāng) and 信 (xìn) literally create the idea of “mutual trust.” While it can mean this, its modern usage has broadened to simply mean “to believe” or “to trust,” even when the action isn't strictly mutual.
The character 信 (xìn) is one of the five core virtues of Confucianism (五常, wǔcháng), representing integrity, trustworthiness, and faithfulness. In Chinese society, being a person of your word is fundamental to building relationships, whether in business or personal life. A person without 信 (xìn) is seen as unreliable and will struggle to gain respect. While 相信 (xiāngxìn) is the everyday verb form, it carries this cultural weight. It's not just a casual word. When you say “我相信你” (Wǒ xiāngxìn nǐ - I believe/trust you), you are making a significant statement about your faith in that person's words or character. Compared to the English word “believe,” 相信 (xiāngxìn) is very similar in most daily contexts. However, the Western concept of “faith,” especially in a religious sense, is often better captured by the more profound term 信仰 (xìnyǎng). You can 相信 God exists (相信有上帝), but your “faith” or belief system is your 信仰. 相信 is the action; 信仰 is the state of being or the system itself.
相信 (xiāngxìn) is an extremely common word used in all registers of speech.
A major point of confusion for learners is the difference between 相信 (xiāngxìn) and 信任 (xìnrèn).
Common Mistake: Using 相信 when you mean “to think” or “to assume incorrectly.” For this, you should use 以为 (yǐwéi).