Other 20th-century philosophers such as Gilbert Ryle and A.J. Ayer were critical of Husserl's concept of intentionality and his many layers of consciousness. Ryle insisted that perceiving is not a process, and Ayer that describing one's knowledge is not to describe mental processes. The effect of these positions is that consciousness is so fully intentional that the mental act has been emptied of all content, and that the idea of pure consciousness is that it is nothing. (Sartre also referred to "consciousness" as "nothing").