On the basis of clinical experience of analysis and psychoanalytical work in a group setting, the idea put forward in this article is that an ideological position is formed each time that the psychic space of a subject, a group or an institution is threatened at its foundations. Thoughts of certainty, necessary to the creation of this space, become rigidly defensive against the Unknown and doubt. We then find the omnipotent Idea, the tyrannical Ideal and the seductive power of the Idol associated in a remarkable configuration. The imperative allegiance to this antisymbolic trinity has as its correlate the exclusion of every other type of thought. Ideology is a systematic construction which purports to provide a universal and total explanation according to a unique principal of causality. These consistent characteristics of ideologies are taken to their extremes in the murderous power of radical ideologies.