When is a spell "cast"?

[0-hr]

If you start a summoning spell, but then all of the bad guys are killed before your next turn comes around, can you abort the spell without losing it?

 

[Beard in the Sky]

I don't think so. Just try having an interesting conversation with your Dire Badger for six seconds before it disappears.

 

[Telperion]

Or, you could use the Dire Badger to keep the other players at bay while you loot the corpses .

 

[frankthedm]

If you start a summoning spell, but then all of the bad guys are killed before your next turn comes around, can you abort the spell without losing it?

Not by the rules.

The various DMs in my group sometimes allow spellcraft checks to save the spell [dc varies], but if blown by 5 points or a natural "1" gets rolled then the critter shows up adjacent and Hostile to the caster.

 

[0-hr]

Not by the rules.

Ok, thanks. Now which page are those rules on?

 

[dcollins]

The key here is that the rules never provide an option to begin a spell and then abort it to get the spell slot back. In every instance (casting a long spell, interrupted casting, casting on defensive) the spell slot is burned once casting begins.

A spell that takes 1 full round to cast is a full-round action. It comes into effect just before the beginning of your turn in the round after you began casting the spell. (PHB, ch. 10: "Casting a Spell: Casting Time")

So that's it. Once you begin casting, you are committed -- a round later the spell effect will appear, and there's no other option given.

Alternatively there's this in the 3.5 SRD:

When you begin a spell that takes 1 round or longer to cast, you must continue the concentration from the current round to just before your turn in the next round (at least).