Laurence has given a good explanation, except that 由此 does not mean hereby. "Hereby" is legal language and means "as a result of this document or utterance". Example: At a marriage ceremony, the priest would say, "I hereby pronounce you man and wife." 我们通常说"由此可见"、"由此可知"，你那句"我们由此可以了解他的为人"有点不伦不类, 写"由此可知他的为人"就行了。 由此可知的"由"，是"凭"的意思，"此"是"这个"的意思。 由此: based on this (evidence, behaviour); relying on this (evidence), (we can infer/conclude/understand …). P.S. Have you thought about learning Chinese directly without using English as an intermediary tool? Using English to learn Chinese will prove to be a great obstacle to you as you progress.

The English translation of 由此 is "hereby", which is fancy language for "from this". 由此可見 is a 4 character phrase that is short for 由此我們可以（看見） / 從那些東西我們可以（看）見 / 從上述的話我們可以（看）見 So it basically means 從剛才說的那（幾）句話我們可以了解他的為人 "From what has just been said we can understand his conduct/behavioir/actions" 因此 just means "as a result". I tend to see 因此 used in structures like 因為___所以____因此____ Laurence