Rationalism is a philosophical approach based on the view that reality has a logical structure accessible to deductive reasoning and proof, and holding, as against empiricism, that reason unsupported by sense experience is a source of "synthetic knowledge" – knowledge, primarily of certain fundamental concepts and principles in logic and mathematics, which, it is argued, cannot be denied without contradiction and yet cannot be dismissed as merely analytic. (See also universals and realism.) Major rationalists in modern philosophy include Descartes, Spinoza, and Leibniz.