Henri de Lubac, Hans Urs von Balthasar, Rowan Williams, Rumi, Ramanuja, Shankara, Maimonides, Ibn Arabi, Sadr al-Din al-Qunawi, Animism, Baháʼí, Dharmic religions (esp. Bhakti, Mahāyāna Buddhism, Vishishtadvaita Vedanta, and Sikhism), Kabbalah, Sufi Islam, and Taoic religions. As indicated by the wide range of topics covered in his essays, Hart has an interest in a diverse range of topics: baseball, Ancient Greek philosophy, patristics, Byzantine philosophy, Catholic theology, Comparative religious studies, Eastern philosophy, Eastern religions, Gnosticism, Hellenistic Judaism, historical criticism, Medieval philosophy, metaphysics, mysticism, myth, The Dreaming, fairies, perennialism, philosophy of mind, theological aesthetics, and world literature. Monism As an outspoken advocate of classical theism as seen, for example, in his book The Experience of God who is also, more generally, engaged with the schools of continental philosophy, idealism, and neoplatonism, Hart also affirms monism. He said in a 17 November 2020 interview about a pre-release reading of his book You Are Gods: At the end of the day, I’m a monist as any sane person is. We can play games with it, but any metaphysics that is coherent is ultimately reducible to a monism. John Milbank in an April 2022 conversation with Hart about You Are Gods said we “agree that in fact neoplatonism and Vedanta and Islamic mysticism are monistic” and “that, actually, an emanationism, a monotheism, these are actually the more monistic visions and that, if we’ve got all these things in Christianity like Trinity, incarnation, grace and deification and so on, these aren’t qualifying monism.” Instead, Milbank said that Hart's book You Are Gods shows that Christianity is spelling out or expounding monism and monotheism. In his book You Are Gods, Hart also describes variations of both dualism and monism that he calls grim and monstrous: An absolute dualism, of course, is a very grim thing indeed; but a narrative monism unqualified by any hint of true gnostic detachment, irony, sedition, or doubt—by any proper sense, that is, that the fashion of this world is horribly out of joint, that we are prisoners of delusion, that not every evil can be accounted for as part of divine necessity—turns out to be at least as monstrous. Universalism Hart's book That All Shall Be Saved was published on September 24, 2019, and makes the case that universalism is the only coherent version of the Christian faith. Although grounded primarily in arguments from Christian metaphysics and moral philosophy, the book