Ready Action Question

[hobbes1020]

Ready action states: Readying is a standard action. You can ready a standard action, a move action, a swift action, or a free action. To do so, specify the action you will take and the conditions under which you will take it.

Let's say a spell caster wants to ready a spell to cast if another caster begins casting. Does this mean that readying an action is a standard action and the casting of the spell is a second standard action thus completing the turn?

Or could the caster first move (move action), and then ready an action with the action being to cast a spell?

[MurphysParadox]

The caster can move and then ready a spell for a specific trigger. The action completes (the spell is cast) when the trigger occurs. You don't gain any additional actions in the round because you used your standard on your turn but didn't complete it until the trigger. If the trigger is not met (no one comes through the doorway, the other guy runs away instead of casting a spell), you lose your readied action.

So on your turn, you move to be able to see the bad guy. You say "I ready dispel magic to counter any spell the bad guy casts". You have now spent your standard action and set up a readied action/trigger. Your turn ends and the bad guy's turn begins.

If the enemy casts a spell, you will cast dispel magic to counter spell.
If the enemy does not cast a spell, you will do nothing.
If the enemy moves behind a wall and casts a spell, you will do nothing because the enemy is no longer a valid target for your spell (no line of sight/effect).

[Are]

Yes, the caster could move, and then ready to cast his spell.

The drawbacks of using readied actions is that if the triggering condition never happens, then you essentially lost that action, plus that even when the triggering condition does happen, your initiative drops.