Passage Summary: We used to treat serious mental illnesses with talk therapy, but now we use medicine. Because medicine works best, these illnesses must be purely biological and have nothing to do with a person's surroundings.

Conclusion: Psychoses are caused strictly by organic conditions and are entirely unrelated to environmental factors.

Reasoning: Psychoses are most effectively treated through medicinal or biochemical means rather than the psychotherapy used for neuroses.

Analysis: The author commits a classic error by confusing the method of treatment with the cause of the condition. Just because a biological intervention (medicine) solves a problem does not mean the problem's origins weren't environmental. You might take a pill to fix a stress-induced ulcer, but that doesn't mean the stress from your job didn't cause it. Look for an answer choice that identifies this failure to consider that environmental factors could still trigger or contribute to organic conditions.