The idea of a transcendental argument has sometimes been held to be Kant's greatest contribution to philosophy. Such arguments can be found before Kant, but nobody was so clear about them or gave them such a central role. Many of Kant's transcendental arguments have been criticised and reconstructed again and again, and new arguments have been devised along similar lines. But there has also been debate about what exactly transcendental arguments are, how they work, and what they can hope to achieve. There is room too for dispute about their role in Kant's own thought. Here an important question concerns the relation between transcendental arguments and transcendental idealism. It is a mistake to think Kant's transcendental arguments led him into transcendental idealism, but it remains interesting to ask how far the use of transcendental arguments does lead toward idealist conclusions. Kant's followers are still divided between those who reject and those who defend the connection.