R. S. Henderson follows the antediluvian Michel Thevoz, Curator of the Collection de l'Art Brut in Lausanne's "Artist Brut", or "outsider artist" premise of those works produced by people who for various reasons have not been culturally indoctrinated or politically conditioned. They are all kinds of dwellers on the fringes of society. Working outside fine art "system" (schools, galleries, museums and so on), these people have produced, from the depths of their own personalities and for themselves and no one else, works of outstanding originality in concept, subject and techniques. They are works that owe nothing to tradition or trend.

A firm distinction should be made between "art brut" and what is known as "naïf art". The naïf or primitive painters remain within the mainstream of painting proper, even if they fail ingenuously to practice its style. However, they accept its subjects, technique (generally oils) and even its values, because they hope for public, if not official recognition. "Art brut" artists, on the other hand, make up their own techniques, often with new means and materials and they create their works for their own use, as a kind of private theatre. They choose subjects who are often enigmatic and they do not care about the good opinion of others, even keeping their work secret.