The exercise is titled ‘De casu ablativo’ and the correct answer to ‘mult_’ is o…so it’s
‘Aedes Iovis Capitolini multo magnifecentior est…’
This is one of those moments in Latin learning when I feel rather disheartened…! I mean surely, to heaven, ‘multo’ is an adverb (‘…much greater’…and not an ablative case of anything…!??
Don’t be disheartened. The ablatives get easier as you progress, they become almost second nature. In this case it is the ablative of degree of difference.
I can recommend the Compendium of Latin Grammar compiled and edited by Andrew Csontos. It provides a good overview of the cases and their uses.
Now that I’m thinking about it, though, the ablative of degree of difference might be quick to recognise, but I can’t recollect a time I’ve seen an adverb used in its place, if that’s at all possible. I’m trying to remember if such a case exists, and tentatively will propose a ‘rule’ that sounds odd even to my ears, only so that someone can tell me if I’m wrong: it might be - and I"ll be quickly corrected here if I’m wrong, which I suspect I may be - that adverbs cannot quantify adjectival comparisons. If someone can throw up a reference for that, either validating or tearing that hypothesis apart, please do!
As an ablative of extent/degree of difference, it merely modifies the meaning of the comparative. E.g. filius multo est altior quam pater - it agrees with neither son nor father, though if you use the ablative of comparison (filius multo est altior patre), patre would in the ablative too. Either way, even if it is morphologically the same as patre, I’m almost certain it stands on its own to adjust the meaning of ‘altior’. Others could include pede (by a foot) or paulo (by a little), for instance; the only issue is confusing one of these for agreeing with the compared in the ablative, as I just said (i.e., thinking ‘the son is taller than the much father’, though understandably there’s not much room for that either).
Thanks Caecilius. Now that I think of it it can’t, given that it’s modifying an adjective, be an adverb as an adverb can only modify a verb. So it seems logical.