由此【yóucǐ】

由此 means "from this". 此 points back at something just mentioned – an event, a fact, a place – and 由 marks it as the source. What follows is a result, a conclusion, or a direction. It is written and formal.

A result

Before a verb such as 引起, 产生, 带来 or 造成, 由此 links a cause to what it set off.

A conclusion

由此看来 and 由此可知 draw a conclusion from what came before: "judging by this", "from this we know". 由此可见 is the most common of these and has its own point.

On signs

On a sign, 由此 means "from here, this way": 由此进入, 由此上楼.

由此 or 所以

由此 belongs to writing, and it needs the earlier fact to be the real source of what follows. For a plain "so" in speech, use 所以.

• × 我饿了，由此去吃饭了 → 我饿了，所以去吃饭了

It is also a different word from 由于 "because", which goes in front of a cause rather than pointing back at one.