Commentary Purg XVIII 28-33

Desire, love in action, now continues by extending toward its goal and remaining in this state as long as it takes pleasure in its appetition.  (For fire as an example of 'natural desire,' see C.Purg.XVII.91-92.)  Thus here Dante is comparing intellectual desire to natural desire, but also insisting on the distance between them.  Natural desire can never be culpable (e.g., fire always 'desires' to rise -- that is its natural inclination).  There is perhaps no moment in the poem of greater danger to its essential philosophical position.  Is human desire -- for money, food, or sexual pleasure -- not as 'natural' as this?  Does anyone not desire these things?  Dante's attempt to persuade us, as he may well have realized, reflects that of another dottore and maestro, Jesus.  He, as the Gospels amply testify, also spoke frequently, in his parables, in terms of human desires that all could understand, e.g., of money, agriculture, marriage.  In all cases the listener is encouraged, even impelled, to understand that such pleasures, as great as they may be, will seem as nothing compared to the joys of Heaven.

      Padoan (Pado.1967.1), pp. 668-70, suggests that Dante's definition of love in this canto intrinsically corrects Francesca's claims for the ineluctable nature of passionate love ([Inf V 103]).

      Dante was surely right to let his language here reflect an essentially sexual view of love.  Consider the last verse of this part of the passage, 'fin che la cosa amata il fa gioire' (as long as it enjoys the thing it loves [for this understanding of the conjunction fin che see Francesco Mazzoni, cited by Bosco/Reggio (DDP Bosco.Purg.XVIII.31-33) in their commentary on this passage; in opposition, reading 'until it attains the thing it loves' as being more Thomistic, see Triolo (Trio.1993.1), p. 268]).  Arriving at this point in the argument, a reader would have to be pardoned for believing that whatever good the spirit of love pursues is ipso facto good, just as the protagonist himself will shortly seem to believe ([Purg XVIII 43-45]).  But what is the nature of the 'moto spiritale' (movement of the spirit) of the 'captive mind'?  That question is reflected in the crucial and concluding portion of Virgil's discourse.