 Condillac’s response to this charge, in his “Lettre de M. l’abbé de Condillac à l’auteur des Lettres à un Américan” (1756, and appended to subsequent editions of the Treatise on Animals) was to claim that, “If I say that our sensations give us an idea of extension, it is only because we take them for qualities of objects when we refer them to something external. But I have proven many times that they certainly do not give us this idea when we consider them as a manner of being of our soul.” This echoes claims made in the Essay and the Treatise. In the Essay, Condillac claimed that we attribute the extension or shape we find in colours to something outside of us rather than to ourselves considered as thinking subjects (I.i.2. §11), presumably because extension is incompatible with the simplicity that must be ascribed to a thinking being. In almost the same breath, he claimed that we are wrong to imagine that the chromatic quality of colours (as opposed to the extension and shape they map out) actually lies on the surface of external objects, purportedly because we have no clear idea of what it would mean for a body to be coloured (I.i.2. §12). But such claims are hardly adequate to avoid the problem and perhaps not even coherent. Either the chromatic qualities that we experience as modifications of our being are extended or they are not. If they are extended, then the claim that we do not recognize this fact when we think of them as modifications of our own being is merely an evasion. If they are not extended, then if we never experience anything other than our own sensations, as Condillac claimed at the outset of the Essay, it is mysterious how we come to attribute extension to external objects.