 But perhaps the most commonly used argument among pantheists has been the ontological argument. As employed by classical theism this line of argument has been much criticised, but the forms in which it has been put forward by pantheists (such as Spinoza and Hegel) are interestingly different. On their way of thinking, the more perfect an idea becomes the less room there remains for any gap between it and its instantiation, but no idea becomes perfect simply by defining itself to be so. This can be shown only by a full development of its content amounting to nothing less than a complete philosophical system (Harrelson 2009).