Dear AZ:

You wrote:
> “Adam dissented from Harry in considering their group a financial
> enterprise.”
>
> Is the above sentence meaningful?
>
> If it is, who is considering the group a financial enterprise? Adam or
> Harry?
>
> If it is Adam, shouldn’t it be “by considering”?
>
> Could the sentence mean they both considered the group a financial
> enterprise but in different ways? They disagreed as to the way in which
> this financial enterprise should be thought of.
>
That is a very stilted sentence. It is the type of sentence we sometimes read when the reader or speaker does not really want us to know the particulars.

You do point out the problem, though. It is not clear whether Adam or Henry considered the group a financial enterprise. You are correct in saying that if you used “by considering,” it would clear that Adam considered the group a financial enterprise and Henry did not. If you wanted to show that it was Henry who considered the group a financial enterprise, then your best bet would be to make Henry possessive–something like “Henry’s view that the group was a financial enterprise.”