Catholic responses to modernism argued that Aquinas's perennial philosophy provided an unsurpassed epistemology to support the rationality of faith. Lydia Schumacher agrees, but excavates the correlate impulse of the Thomistic synthesis, that theological ontology secures the rationality of reason, which is presupposed by non‐theistic philosophers. The suggestion—obviously provocative—is that, even as secularised philosophy demands from theologians an account of their discipline's conformity to the canons of reason, theologians should interrogate philosophy as to the origin and basis of its claims to rationality (if not from some account of a transcendent good, then from where?). Comprising a diptych with her earlier Rationality as Virtue, Theological Philosophy again evinces Schumacher's creativity in drawing her mastery of Thomistic thought into dialogue with contemporary philosophical questions. The implications of Schumacher's proposals are wide‐ranging, not because she offers an unproblematic resolution, but because she indicates with an incisive clarity the direction of travel towards a renewal of Christian philosophy and a more honest appraisal of philosophy's intrinsic limitations.

The thought of Aquinas is omnipresent in Theological Philosophy, not least in the account of the virtues as the (re‐)integrating tools of both the intellectual creature's natural harmony and their supernatural reditus to God. Above all, it is the predominance of Thomistic intellectualism that animates her work: rationality and the moral life coinhere, intellectual virtue has a moral end and rationality is ‘deficient […] when the commitment to the highest good that constitutes rationality is inconsistent’. This moral‐intellectualism is conjoined with an ‘ontology of becoming’, in which humans are ordained to a state of constant movement towards realisation of their created nature, by the cultivation of rationality now conceived as intellectual virtue. The reditus to God of the supernatural life, then, implies fidelity to the exitus of creation. There are hints of a Rahnerian subjectivity here, with finite creaturely knowledge seeming to grasp towards the infinite and asymptotic horizon of all our mental (and moral) activity. But if Rahner's Vorgriff auf esse seems to prioritise intellectus, Schumacher seems more comfortable with ratio. In part, this is because Schumacher situates her point of departure more firmly within the embodied finitude of creatureliness than does Rahner: her investigation focusses on rationality under temporal and fallen conditions (hence her monotonous return to virtue as intellectual therapy). The beatific vision, as the eschatological consummation of the created intellect, should, however, have a greater prominence in the argument, particularly in investigating creedal reasoning about the redemption. Developments of Schumacher's thought will need to say more about the unthematic aspects of knowledge, particularly intuition and Newman's ‘illative sense’, but Schumacher has prepared a way for this in her treatment of affectivity and desire, not least in the examination of the theological virtue of hope.

With rationality given a moral (and thus teleological) constitution as commitment to the highest good (pp. 47‐56), the transition from pro‐theological philosophy to a fully theological philosophy can unfold, as if by the quinque viæ: the definition ‘of rationality in terms of intellectual and moral virtue is ultimately a theological philosophy precisely because of […] the divine transcendence’ (p. 65). Some will see a circularity here: rationality‐as‐virtue presupposes the theological philosophy, which is itself derived from the account of rationality that it defends. Natural theology has a role to play in breaking this circularity (bringing with it an affirmation of the analogy of being, grounded in the doctrine of participation). The divine simplicity, knowable by natural reasoning, is precisely the highest good that is the asymptotic term constitutive of created rationality; its unity and eternity necessarily differentiating it from ersatz transcendence. Hints towards this absolute transcendence as the sine qua non of rationality can, it seems, be discerned from reflection on human rationality ab intra (but dealing with Kant is not much in evidence). The Trinity, unknowable to unaided human reason, is a more perfect expression of the transcendent ground of rationality, in that it affirms the capacity of the supreme good for self‐communication. In turn, this self‐communication of the infinite Good is actualised in respect of human creatures in the Incarnate Word. These metaphysical ‘necessary conditions’ are reflected in the correlate transition from the cardinal virtues as ‘preconditions’ to the theological virtues as ‘sufficient conditions’.

As the structure of Schumacher's argument makes clear, this transition does not render the cardinal virtues as a mere propadeutic, untouched by grace and left behind in a mystical advance: charity is the form of the virtues (p. 163). A consequence of the theologal life of the sufficient conditions is that the cardinal virtues operate with a new lustre, an ‘optimized capacity’. Here it is clear that grace perfects nature without destroying it, but where is the ‘entry point’, where grace and revelation enter to compensate for the failure of nature's innate capacities? Schumacher's account of simplicity, Trinity and incarnation as necessary metaphysical conditions of theological philosophy is well argued, but it seems they can only be known as such within such an antecedent revelation: perhaps Gottlieb Söhngen's ‘analogia entis within an analogia fidei’ could express this. It is, however, hard to shake off the sense of supernature having been naturalised and that philosophy is always already theology; there is something more than nature as ‘open upwards’ to the divine here. The way in which Schumacher's arguments implicitly debunk myths of secularised reason and hint towards the necessary openness of the philosophical to theology is almost Blondellian, even if Schumacher is quick to affirm that there can be rationality outside of explicit faith.

The diptych coheres around a participatory reading of Aquinas, mediated by Rudi te Velde, and used to differentiate the metaphysically necessary authentic transcendence from the faux transcendence of ontotheology and pantheism. ‘Theology alone can delineate the transcendent conditions for the natural’ (p. 191)—or as John Milbank has put it ‘only theology overcomes metaphysics’. Is it wrong to read Schumacher's diptych as a more trenchantly Aristotelian alternative to Radical Orthodoxy? Either way, her extraordinary work is of a commensurate stature and deserves equally wide reading.