*Thereby : así de este modo
Robert sabotaged the project. thereby ensuring it would fail
Therein: en eso, alli dentro
The report and all claims therein has not been verified by them (therein→dentro de él)
The plan is affordable, and therein lies its strength (therein→y en ello)
Thereof: del mismo, de eso, de esto
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Therefore: por lo tanto, por eso, luego
I think, therefore I am
Wherein: de qué manera, en qué forma
Wherein do you object to these proposals?
Whereby: a través del cual, por el cual
The bank manager was at a loss to understand the means whereby the thieves had entered the vault
Hereby: por la presente
The head juror stood up and said, "The jury hereby declares the defendant guilty"
Thereafter: a partir de ahí
The manager made it clear that she wouldn't tolerate anyone being late for work and no one was late thereafter
* Thereby:
- If I use thereby with -ing form I have to place a comma before it
- If I use it after a coordinating conjunction, I have to use past or present
The team lost the final game of the season, thereby missing the play off
Lisa studied for three straight weeks and was thereby able to pass her test
You can see a really good explanation here.