As a conjunction, "以" is used to indicate a condition, reason, or basis for something. For example: 以我所知,他已经离开了。 (Yǐ wǒ suǒ zhī, tā yǐjīng líkāile.) — From what I know, he has already left. (lit. According to what I know, he has already left.) 以他的智慧,这个问题不难解决。