"if a future state be clearly proved, does it follow that it
will be a state of punishment or reward?"

Then in extension of the same argument he urges:

"Sleep suspends many of the faculties of the vital and
intellectual principle--drunkenness and disease will either
temporarily or permanently derange them. Madness, or
idiotcy, may utterly extinguish the most excellent and
delicate of these powers. In old age the mind gradually
withers; and as it grew and strengthened with the body, so
does it with the body sink into decrepitude."

He also considered that:

"It is probable that what we call thought is not an actual
being, but no more than the relation between certain parts
of that infinitely varied mass, of which the rest of the
universe is composed, and which ceases to exist so soon as
those parts change their position with regard to each other.
Thus color, and sound, and taste, and odor, exist only
relatively."

Even granted that mind or thought be a part of, or in fact, the soul,
then he asks in what manner it could be made a proof of its
imperishability, as all that we see or know perishes and is changed.

Here then comes the query, "Have we existed before birth?" A difficult
possibility to conceive of individual intelligence and if unprovable
against the theory of existence after death.