This study is concerned with the spiritual impetus and the lived dimension of the philosophy of the French Thomist Jacques Maritain in light of John Caputo's Heideggerian critique of Thomist metaphysics. In Heidegger and Aquinas: An Essay on Overcoming Metaphysics, Caputo argues that the thought of Thomas Aquinas, probably the most important and most representative figure of orthodox Catholic thinking, is a paradigmatic case of what Martin Heidegger calls 'ontotheology'. This is the dominating tendency of Western philosophy and theology to view Being not as a mystery, but metaphysically as a mere collection of things which are simply present- external to the human being and the value of which is use. For Aquinas, according to Caputo, God is the highest 'being' that creates other 'beings', and it is in virtue of this relationship that human beings, allegedly made in God's image, view the world simply as a collection of things to be manipulated. The first question constituting this study's point of departure, then, is: if Aquinas is indeed an exemplar of ontotheological thinking, is the same true of Jacques Maritain, perhaps the twentieth century's most influential follower and interpreter of Thomas Aquinas? Yet in the same work Caputo also proclaims that what has been said is not the whole truth about Aquinas, and the argument that his thought is an instance of ontotheology is in fact what Caputo sets out to respond to-for the sake of recovering an Aquinas who was not a 'cold rationalist', but a spiritually gifted contemplative, a Catholic saint. Caputo makes the case that we can, by employing a method of 'retrieval' or 'deconstruction'-inspired by Heidegger and Jacques Derrida-find that which is hidden or left 'unthought' in Aquinas but which nevertheless determines his entire philosophical and religious life. This, Caputo argues, is a pre-metaphysical, mystical tendency directed towards the mystery of being, which overcomes metaphysics and escapes ontotheology. Here I apply this Heideggerian critique and retrieval to Maritain, and I argue that while there is in Maritain the same 'ontotheological' tendency to view reality as a collection of things and God as paradigmatic maker of things-the prima causa so richly expressed in Thomistic doctrines of the 'transcendentals' and participative being-there is in him a deep pre-metaphysical, mystical tendency which is, in fact, far more explicit than in Aquinas. In the first part of the study, I compare the philosophical doctrines and projects of Maritain and his first teacher and guide, Henri Bergson, and then of Heidegger in relation to Maritain. I also give a sketch of Maritain's religious and intellectual development, identifying the key religious and artistic figures involved: the novelist Léon Bloy and the painter Georges Rouault. In light of the philosophical analyses and what can be gleaned from Maritain's biographical notes, his correspondence, and the biographical insights provided by those close to him, I argue that we can see in Maritain the same concern for the question of the meaning of being in relation to human life that we find in Heidegger, and that, like Heidegger, this concern underlies his philosophical thought and serves as the impetus for something beyond philosophy. I show that from his Bergsonian beginnings to his later days as a Little Brother of Jesus, Maritain has a profound sense of the pre-conceptual and intuitive kinds of knowledge that we find in existentialist thinkers such as Heidegger, and also artists and mystics. I posit that while Maritain claims what he calls the 'intuition of being' is the most primordial experience human beings can have of ultimate reality, there is, in fact, an experience, or aspiration to have such an experience, which is even more basic, with greater implications for overcoming metaphysics and ontotheology: mystical communion with ultimate reality. The aspiration for such communion is, I claim, the 'unthought' in Maritain that must be sought out for the purpose of retrieving a Maritain who goes beyond metaphysics. Mapping out the main branches of Maritain's thinking about being in terms of the classical doctrine of the 'transcendentals' and corresponding instances of connatural knowledge, the second part of the study is devoted to finding where, in Maritain's thought, a retrieval might be possible. Examining Maritain's conceptions of the connatural experience-knowledge of the moral good and mystical experience, I conclude that we cannot discover any overcoming of metaphysics and ontotheology in either when they are taken on their own terms. For underlying both conceptions, I claim, is Maritain's 'master concept' of the 'act of existence', or esse, the metaphysical principle which makes it possible for the human being to take hold of their own existence and participate in the moral and divine life. The distinction between esse and the essence of beings (essentia) and a stress on the former, as Caputo argues with regard to Aquinas, in fact only supports Heidegger's thesis on the ontotheological character of Thomist thought. For a stress on esse, the principle by which God creates and sustains things in existence is only the outcome of a preoccupation with conceiving God primarily as the 'maker' of things. And what of esse when it comes to mystical experience? Mystical experience, Maritain says, is that of which metaphysical wisdom 'awakens a desire' even while it is unable to attain it, such that the testimony of it, such as that provided by St. John of the Cross, 'no philosophical commentary will ever efface'. Yet here, too, esse only serves to make an unbridgeable ontological and cognitive divide between God as viewed in terms of His causal transcendence and as an intentional object of consciousness, as presence- something or someone external to oneself. This is so even as one is, in virtue of the connatural experience-knowledge of love, united with Him in 'one spirit', as Maritain says, following St. John of the Cross. Given this, I seek a retrieval of Maritain elsewhere, in the richest and most original areas of his thought: the connatural experience-knowledge of the artist and the relationship between the artist and the mystic. For Maritain, true artists and mystics are not concerned with reducing reality to manageable chunks but with expressing the mystery of reality, and, as I demonstrate in the final two chapters, it is when the vocations of the Catholic artist and the Catholic mystic converge in Maritain's reflections-in the cases of Léon Bloy, St. John of the Cross, and Maritain's wife Raïssa-that we are able to retrieve a Maritain that, while very much remaining a Catholic philosopher, is also a mystic. I claim that it is when his thought is situated in its wider existential and religious context that Maritain as both thinker and contemplative escapes the charge of ontotheology because there exists in him a primordial and utterly determining mystical aspiration to experience a communion in love with ultimate reality, best expressed in terms of poetic and mystical language, rather than the metaphysical language of Thomist philosophy. Essential in demonstrating this are events in Maritain's life as well as people-artists and mystics-who reveal the mystery of Being to him. Toward the end of the study, I claim that this immanent mysticism in Maritain-which, unlike that of Caputo's retrieved Aquinas-balances apophatic and cataphatic elements and, as such, is complex and profound enough to render the categories of contemporary debate on the nature of mysticism and mystical experience in need of revision.