Before we continue with what this chapter really is about, pronouns, we have to make a small loop to discuss a related phenomenon: The pronominal adverb.
The pronominal adverb, or 'pronoun adverb', is not a complete novelty to English speakers:
"Whereof one cannot speak, thereof one must be silent"
--Ludwig Wittgenstein
"I know a bank whereon the wild thyme blows"
--William Shakespeare
We use it in modern English too:
"I am hereby sending you the details of your order."
"Therefore, we decided to postpone the project."
The mechanism
Whereof is another way of saying 'of which'. Hereby is 'by this', therefore is 'for that', and so on.
If the pronoun what/which, this, or that is preceded by a preposition (of, by, for), we can replace the pronoun by the adverb where, here, or there.
Note that we can only do this to pronouns that refer to inanimate things, not to persons.
Which/what turns into where:
| whereof
| of what
|
| wherewith
| with what
|
This turns into here:
| hereon
| on this
|
| hereby
| by this
|
That turns into there:
| thereof
| of that
|
| therefore
| for that
|
On the next page, we will look at the Dutch pronominal adverbs.
Questions? 
