The Grammar of “Also”

A reader once sent me the following sentences and asked which was correct and why:

The research also must be validated.

The research must also be validated.

Also is like only in that both are what The Cambridge Grammar of the English Language calls “focusing modifiers”: their position in the sentence determines which element in the sentence they focus on. 

Focusing modifiers can occupy several positions in the sentence, causing either ambiguity or clarity. Like real estate, also’...