Quick questions about Summon Monster

[Jimp]

1. The list of monsters you can summon for the Summon Monster X spells in the PHB lists various celestial and fiendish versions of animals, such as a Celestial Dog. Is there any rule against summoning a Fiendish Dog instead?

2. Can you summon creatures not on the lists given? If so, how do you know which creatures are suitable?

[Pegasos989]

1. The list of monsters you can summon for the Summon Monster X spells in the PHB lists various celestial and fiendish versions of animals, such as a Celestial Dog. Is there any rule against summoning a Fiendish Dog instead?

2. Can you summon creatures not on the lists given? If so, how do you know which creatures are suitable?

By RaW, you can do neither.

They are divided so that certain aligned casters get access to certain monsters, because monsters have diffrent special abilities and it might be broken to combine them... Nah, I am just kidding - neutral aligned casters get already access to every monster there and fiendish and celestial templates aren't that diffrent in power. I don't think that houseruling it possible would affect game balance.

On the second... You can't by raw and should determine it with your DM. However, all summoned monsters of the same level spell seem to have nearly the same CR so it is somewhat working guideline. It should be evaluated case by case basis, however.