This article givesaclear presentation of the key contributions of the Summa Halensis at the outset of the 13 th century debates over the reason for the incarnation (ratio incarnationis)a mong Franciscans at the University of Paris. Moving from Alexander of Hales to the Summa Halensis,the article shows the brothers' two signal contributions:1.t he categories of necessity and fittingness,s et out at the outset of their commentary on the Lombard'sthird book of Sentences,set aframe for their

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... ion of the reason for the incarnation, and 2. an advanced appreciation for the problems counterfactual reflection presents for divinefreedom. Finally, the brothers' contributions are shown to recievefurther development in OdoRigaldus' subsequent reflections on the reason for the incarnation. If therewerenofall, would therebeanincarnation? Our earliest recordofthis counterfactual, which sparkedthe historic 13 th -century debates over the reason for the incarnation( ratio incarnationis), occurs earlyi nt he 12 th century in Ruperto fD eutz's commentary on Matthew'sG ospel, De gloria et honore Filii hominis.¹ He giveso nly ac ursory answer to this question. The first extended discussion of the question was produced sometime between 1230 and 1235 by Robert Grosseteste in Book 3o fDe cessatione legalium.² Grosseteste'st reatment is roughlyc ontemporaneous with Alexander of Hales' far briefer treatment of the question in his Quaestiones disputatae 'antequam essetf rater' (Qu.d isp.).³ Both texts predatet he treatment of the counterfactual question in Book 3o ft he Summa Halensis. The Summa Halensis marks an important moment in the history of the reason for the incarnation. When the authorso ft he Summa placed the counterfactual in the opening questions of Summa Halensis III, theye stablished it as ac ommon point of disputation for theologians commenting the Lombard's Sentences. After the Summa Halensis,itwas standard to consider the question in the opening distinctions of Book 3, until it was moved by John Duns Scotus to the discussion of Christ'sp re-