Rahner privileges the question as the starting point of his transcendental enquiry, and proceeds to expose its conditions of possibility through a transcendental reflection. Ultimately, the supreme transcendental condition of possibility is absolute being which is demanded by and sustains the dynamism of the spirit.
Whereas Kant's transcendental reflection was formal and static, Rahner, following Maréchal, focuses on the act or performance (Vollzug) of knowledge which shows itself to be a constant movement of transcendence. Thus, although the ontology which sustains Rahnerian epistemology is one in which Being and knowing are essentially related, nonetheless, the finite spirit is less to be understood in terms of self-presence, but rather, and more primordially, as transcendence towards what is other than the subject, towards the alterity of exteriority.
Theologically, the relation with alterity is experienced in the proximity of grace, in which God communicates himself to the essentially open and receptive subject, while remaining himself uncompromised by his offer.
The difficulty of an ontological approach which associates being and knowing is that it tends to reduce human spirituality to the level of the cognitive, whereas the relationship with what is other than the subject, the alterity of exteriority, is not only cognitive but also affective and volitional. This surely is what Levinas reacts against in his ongoing implicit criticism of the ontotheological tradition which culminates, for him, in Heidegger, and why he seeks a sense in sensibility in terms of openness and vulnerability rather than the cognitive. Levinas, too, reacts against the notion of the "whole" or the totality and privileges the "idea of infinity" which is unencompassable by the "whole". It is the ethical relationship with the Other rather than the ontological relation of a being and Being which needs to be phenomenologically reduced, a reduction which Levinas pursues by following through Husserl's phenomenological analysis of the inadequacy of evidence and awakening it to the intersubjective level. In the face of the tendency to adequate being and knowing, Husserl's insight is the inadequacy of evidence.
We saw this too in the notion of the question, from which both Rahner and Heidegger begin their enquiry. In the same way that Levinas criticises Husserl for halting his reduction prematurely, we