Can be a compulsive urge to do something (compulsion neurosis), but also certain fears (phobia) can become an obsession. Also certain thoughts, words or fantasies may recur persistently in the consciousness; the patient may not wish to think the thought, but still it comes. A harmless example is a song which keeps repeating itself in the mind. Less harmless are obsessive thoughts which the patient finds a torment. Obsessions can also cause guilt feelings: they can often be blasphemous or obscene, or concerned with wishing to murder someone. It would therefore seem that obsessions are usually based on repressed impulses (defence mechanisms). Obsessions often occur in neurosis, in which case the treatment is also psychotherapy, aimed at the complete neurosis.