An obsession is defined as an idea impulse or image which intrudes into the conscious awareness repeatedly, it is recognised as irrational and absurd, the patient tries to resist against it but is unable to, failure to resist leads to marked distress. An obsession is usually associated with compulsion and a compulsion is defined as a form of behaviour which usually follows obsession, the behaviour is not realistic and is either irrational or excessive. Compulsion may diminish the anxiety associated with obsession (Ref: a sho textbook of psychiatry, Niraj Ahuja, 7th edition, pg no.95)