A theme Wallace Stevens goes back to over and over is that the defining factor of the world we live in isn't really the world itself, but the way we perceive it. We see the world the way we are, not the way it is.
This is the main theme in Anecdote of the Jar, and Thirteen Ways of Looking at a Blackbird; it is probably the main theme of The Blue Guitar. It is an important theme even in poems which have other main messages, including The Emperor of Ice Cream and Sunday Morning.
Stevens most famous formulation of his poetic creed:
The poem must resist the intelligence / Almost successfully
suggests that he was particularly influenced by the poetry as magic ideas which are characteristic of the end of the nineteenth century in France, probably begin with Rimbaud, but come to their fullest fruition in Laforgue. (Mallarmé's semantic / syntactic experimentation - especially in Un Coup de Dés - also seems to be visible in much of Stevens' work).
In many ways it is useful to see Wallace Stevens as continuing the mysticism of Laforgue, while T S Eliot continues Laforgue's equally central interest in natural language and the use of humour for serious purposes in a poem.
