In both his published and unpublished works, Edmund Husserl, the "father of phenomenology," struggles repeatedly with the relation of the individual subject and intersubjectivity. Since his phenomenology is based upon the temporalizing foundations of the subject, though, he is often accused of solipsism, and his efforts at integrating the subject with an intersubjective existence are registered as falling short of their goal. Important philosophers who use phenomenology as their basis, such as Martin Heidegger and Maurice Merleau-Ponty, furthermore, while implicitly criticizing his limitations, assume the existence of intersubjective foundations without taking up the existence and formation of these foundations themselves.