Person

Bonaventure

Italian Franciscan friar, theologian, and philosopher; Minister General of the Franciscan Order (1257-1274); declared Doctor of the Church in 1588 (the Seraphic Doctor). A near-exact contemporary of Thomas Aquinas at the University of Paris, Bonaventure represents the Augustinian-Platonist wing of high scholasticism, emphasizing illumination, divine exemplarity, the affective ascent of the mind to God, and a via mystica over the Aristotelian-empirical via demonstrativa favored by the Dominicans. His major doctrinal works (Commentary on the Sentences, c. 1250-52; the Breviloquium, 1257; the Itinerarium Mentis in Deum, 1259) became the standard Franciscan textbook tradition.

Position in the codex's framework

Bonaventure is a medieval voice for the necessity of a temporal beginning of the universe, distinguishing him sharply from Aquinas, who held that an eternal-yet-created universe is philosophically possible (though we know by revelation that creation is temporal). The Bonaventure-Aquinas disagreement is one of the most cited cases in medieval cosmological theology and connects directly to the contemporary Kalam Cosmological Argument:

Bonaventure (Commentary on II Sentences, d. 1, p. 1, a. 1, q. 2): argues that the universe cannot be eternal even in principle, an infinite past would require an actually-infinite-completed set of past durations (he prefigures the modern impossibility-of-actual-infinite-past argument); past durations can be counted from the present backward; one cannot add to an actual infinite; etc. Several of his arguments are direct ancestors of William Lane Craig's kalam revival.
Aquinas (ST I q. 46 a. 2): argues that an eternal created universe is philosophically possible (a universe could be eternally dependent on God); we know creation is temporal only by revelation. The disagreement is not over whether creation happened, both affirm it, but over whether philosophical reason alone can prove it.

The Bonaventure side is the historic source of the strong philosophical case for a beginning, which contemporary kalam defenders revive against eternal-universe and oscillating-universe cosmologies. See Kalam Cosmological Argument.

Other relevant positions

Hexaemeral exegesis: Bonaventure's Collations on the Six Days (Collationes in Hexaemeron, 1273) is a sustained mystical reading of Genesis 1 as the structure of all reality, neither strict 24-hour creationism nor full Augustinian instantaneous-creation, but an exemplarist Christology in which the six days unfold the divine Word's reflection in creation. See Genesis Interpretation Spread § patristic context, Bonaventure is one of the medieval witnesses to non-uniform reading of Genesis 1.
Divine exemplarity: every created being mirrors a ratio aeterna (eternal idea) in the divine mind; the cosmos is theophanic, every creature a "footprint" (vestigium) or "image" (imago) of God. The framework grounds his sacramental ontology and shapes much of medieval Franciscan natural theology.
Mystical ascent: the Itinerarium Mentis in Deum lays out a six-stage ascent through created reality, the soul, and divine names into mystical union, one of the foundational texts of Western contemplative theology.

Major works

Commentary on the Sentences of Peter Lombard (c. 1250-52), academic systematic theology
Breviloquium (1257), compact summa of Franciscan theology
Itinerarium Mentis in Deum (1259), six-stage mystical ascent
Legenda Maior (1263), official biography of Francis of Assisi
Collationes in Hexaemeron (1273), unfinished lectures on Genesis 1 / cosmic exemplarity
Quaestiones Disputatae de Mysterio Trinitatis

Reception

Made Doctor of the Church (1588); patron of the Franciscan order; cited by Catholic encyclical tradition through Leo XIII's Aeterni Patris (1879).
The Augustinian-Platonist wing he represents was eclipsed in Catholic theology by the 19th-century Thomistic revival but never disappeared; recent retrievals (Joseph Ratzinger / Benedict XVI's habilitation thesis was on Bonaventure's theology of history; Jean-Luc Marion, Hans Urs von Balthasar) have re-centered his thought.
His cosmological-temporal-beginning argument was largely forgotten until William Lane Craig's The Kalam Cosmological Argument (1979) revived it; Craig credits Bonaventure as a direct medieval precursor.