a. The construction with quam is required when the first of things compared is not in the Nominative or Accusative.[This is a branch of the Ablative of Separation. The object with which anything is compared is the starting-point from which we reckon. Thus, ``Cicero is eloquent'', but, starting from him, we come in Cato, who is ``more so than he.'']
NOTE 1: There are several limitations on the use of the ablative of comparison even when the first of the things compared is in the nominative or accusative.
The quam construction is regularly used (1) when the comparative is in agreement with a genitive, dative, or ablative: as, - senex est eó melióre condicióne quam aduléscéns (Cat. M. 68), an old man is in this respect in a better position than a young man; and (2) when the second member of the comparison is modified by a clause: as, - minor fuit aliquantó is quí prímus fábulam dedit quam eí quí, etc. (Brut. 73), he who presented a play was somewhat younger than those who, etc.
NOTE 2: The poets sometimes use the ablative of comparison where the prose construction requires quam: as, - páne egeó iam mellítís potióre placentís (Hor. Ep. 1. 10. 11), I now want bread better than honey-cakes.
NOTE 3: Relative pronouns having a definite antecedent never take quam in this construction, but always the ablative: as, - réx erat Aenéás nóbís, quó iústior alter nec, etc. (Aen. i. 544), AEneas was our king, than whom no other [was] more righteous.
b. In sentences expressing or implying a general negative the ablative (rather than quam) is the regular construction when the first member of the comparison is in the nominative or accusative: -
c. After the comparatives plas, minus, amplius, longius, without quam, a word of measure or num er is often used with no change in its case: -
NOTE: The noun takes the case required by the context, without reference to the comparative, which is in a sort of apposition: ``seven hundred were taken [and] more.''
d. Alius is sometimes followed by the ablative in poetic and colloquial use; in formal prose it is followed by ac (atque), et, more rarely by nisi, quam: -
e. The comparative of an adverb is usually followed by quam, rarely by the ablative except in poetry: -
NOTE: Prepositions meaning before or beyond (as ante, prae, praeter, suprá) are sometimes used with a comparative: as, - scelere ante aliós immánior omnís (Aen. i. 347), more monstrous in crime than all other men.