 Among Descartes’ persistent themes is that such preconceived opinions can obscure our mental vision of innate principles: that where there are disputes about first principles, it is not “because one man’s faculty of knowledge extends more widely than another’s, but because the common notions are in conflict with the preconceived opinions of some people who, as a result, cannot easily grasp them”; whereas, “we cannot fail to know them [innate common notions] when the occasion for thinking about them arises, provided that we are not blinded by preconceived opinions” (Prin. 1:49f, AT 8a:24, CSM 1:209). These “preconceived opinions” must be “set aside,” says Descartes, “in order to lay the first foundations of philosophy” (May 1643 letter to Voetius, AT 8b:37, CSMK 221). Otherwise, we’re apt to regard, as first principles, the mistaken (though prima facie obvious) sensory claims that particularists find attractive. Such mistakes in the laying of the foundations weaken the entire edifice. Descartes adds: