Amber asked:

In your tenth set of questions and answers, question number 82 intrigued me. To further explore this,
how does philosophy deal with altered perceptions and realties? For example, drug addicts, people
with psychological problems, etc?

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Both views mentioned in the answer you refer to — the Lockean theory that concepts are gained from
sensory ideas and the alternative Kantian position that mental activity rather than sensations are the
ground of belief — seem to be compatible with our understanding of drug addicts and people with
psychological problems.

Suppose that what we see are mental images which resemble reality and we thereby form concepts
about the empirical world, then drug addicts and people with psychological problems need not differ
in this respect: They speak our language and possess the same concepts. While under the influence
of drugs, perceptions may not resemble reality and understanding may be temporarily impaired but
that doesn't affect a theory about how concepts are acquired. If someone was fed LSD from birth their
sensory experiences would probably diminish in robustness as time passed making the acquisition of
concepts impossible, which Locke would predict. As with drug addicts, people with psychological
problems normally have conceptual understanding. I don't think psychological problems which affect
sensory experiences emerge in young children so it would be possible to acquire concepts in the way
empiricists describe. Apparently, schizophrenia is an adult illness so a person could acquire concepts
as a child. But as Locke would predict, if it were the case that a person was born with schizophrenia,
not all of their sensory experiences would resemble reality.

As for the Kantian approach, we don't suppose the baby fed LSD or the schizophrenic baby are going
to develop differently structured understanding leading to some different sort of mental activity. If
there are abnormal sensory experiences, these will be beyond understanding, but they do not change
what understanding is. Some psychological problems do involve mental activities which interfere with
the understanding of others, such as the use of defence mechanisms, but these activities are not
conceptual but emotional. Fear and anxiety have been held to lead to the defence mechanism of
destructive behaviour but the activity in the mind that leads to destructive behaviour and is
responsible for fear or the feeling of being persecuted is driven by emotional forces. Understanding
and conceptual development are rational rather than emotional and are structures which can be
interfered with by emotional imbalance, but the means by which we understand the empirical world
doesn't change.

Rachel Browne