Do I need line of sight to ready an action?

Question

While readying an action, one needs to chose which action he wants to take and (if applicable) on which target.

Can I target a generic "the next creature that becomes a valid target" or do I need to be more specific and choose a specific creature like "When Tordek the fighter comes into line of effect/sight/both"?

Is being able to see or having line of effect towards Tordek necessary to choose him as a target while I take the Ready an Action action (I'm not talking about when I take the readied action as a reaction, I'm talking during my own turn when I decide to ready)?

Answer 1

Line of sight is not a requirement, but being aware of the creature is (probably).

The requirements for ready an action (PHB, p291) include three things you have to choose: the action, the intended target and the trigger. The second part is the important one, but this is where it gets a bit muddy.

Both examples provided in the action's description include naming a specific creature (the troll, the goblin) as part of a ready an action declaration. The words "the intended target" do imply that you need to pick the specific target beforehand when readying the action, and just a "I'll use melee basic attack on the next creature that moves next to me" wouldn't work. In this case, you do need to be aware of the creature to name it as a target.

That's just an implication, however, and I'm sure some GMs will allow a wording such as the one above. In that case, awareness at the moment of picking the readied action is not necessary as the target only becomes selected at the moment of the trigger firing off.

In both cases, line of sight or line of effect are not a requirement - because, RAW, they apply specifically only for targets you attack or spaces you create an effect in. Choosing a target for the ready an action action is neither.

Answer 2

Good question!

The rules aren't so clear:

PHB pg 291:

When you ready an action, you prepare to react to a creature’s action or an event.

[...]

Choose the specific action you are readying (what attack you plan to use, for example) as well as your intended target.

It say to choose the target, but in Dungeon Master's Kit DM's book pg 160 the rule is slightly different:

Choose the specific action the creature is readying (the attack it plans to use, for example), as well as the intended target, if applicable.

The target is become almost optional.

Also look the example (in either sources):

As soon as the troll walks out from behind the corner...

If the troll is behind the corner you don't have line of sight to him, right? You know that a troll is there but you don't see him.

Don't forget that in D&D4° the players have many informations so when the encounter begins the DM probabily places all the monsters on the board and the player know about them and he can acts in conseguence, even if they are out of sight for the PC.

BTW 'the creature who walks out of the corner' IS a target and is specific. Nowhere say to name it.

Finally you can ready an action to react to a creature’s action or to an event. You RAW can consider 'When a creature becomes a valid target' like an event and ready an action against him.

Answer 3

I haven't played 4e in a while so I'm working off of the way readied actions work in 3.5 and 5e which don't seem to have changed much.

No, you probably don't need line of sight to Tordek when you're readying an action, just like you wouldn't need to be able to see something to plan a sequence of events on your part in real life.

Your character does need to be aware that something might come around the corner.

As far as the second part, were I to DM, I'd be tempted to take "next creature that becomes a valid target" a little more broadly than the player might like, since that might be an ally. Precision is definetly appreciated as a GM, simply because it's easier to work with. Broad and ambiguous conditions for readied actions are kind of a pain.

So you don't need to be as precise as "Tordek the figher" but if you're dealing with a number of foes "the next foe to come around the corner" might be better than "the next valid target" since you're now defining what you believe to be a valid target, and it leaves the GM a little room for chicanery if your character is unaware that Malborn the Wizard is actually a disguised doppelganger.

Hope that helps.