On the other hand, into modern times some philosophers have continued to propose that the human mind has an in-born ("a priori") ability to know the truth conclusively, and these philosophers have needed to argue that the human mind has direct and intuitive ideas about nature, and this means it can not be limited entirely to what can be known from sense perception. Amongst the early modern philosophers, some such as Descartes, Spinoza, Leibniz, and Kant, tend to be distinguished from the empiricists as rationalists, and to some extent at least some of them are called idealists, and their writings on the intellect or understanding present various doubts about empiricism, and in some cases they argued for positions which appear more similar to those of medieval and classical philosophers.