Mental Illness is defined as

• A. A medical condition that affects a person's feeling, mood, thinking, and ability to relate to others on occasion
• B. A medical condition that only affects a person's mood and thinking
• C. A medical condition that affects a person's thinking, feeling, mood, and ability to relate to others, disrupting daily function
• D. A medical condition that affects a person's mood and feeling, but can still relate to others

Answer: (C)

Mental illness is a medical condition that affects how a person thinks, feels, and behaves, and it often changes how they relate to others. The best choice includes all four areas—thinking, feeling, mood, and the ability to relate to others—and adds that these problems disrupt daily functioning. That emphasis on impairment in everyday life is what distinguishes mental illness from temporary distress or a limited mood issue.

If a description says it happens only on occasion, it misses the persistent and disrupting nature of many mental illnesses. If it focuses just on mood and thinking, it leaves out how relationships and daily functioning can be affected. If it mentions mood and feeling but allows someone to relate to others normally, it implies there’s no impairment, which doesn’t fit the usual understanding of mental illness.