Instead of fighting right away, he used his brains.

他没有立即战斗， 而是动用了脑筋。

" I think, therefore I am." So he was saying because he knows he's using his brain to think, that proves to him that he exists, that he is, because he thinks.

“ 我思故我在。 ” 所以他说因为他知道他在用他的大脑思考，这向他证明他存在， 他存在，因为他在思考。

No, Isak must use his brains to find a way. The whole thing had come about somehow without their knowing; maybe the wedding business was just as important as the christening—how should he know?

不行，Isak 必须动动脑筋想办法。整件事是在他们不知情的情况下发生的。也许婚礼生意和洗礼一样重要——他怎么知道的？