This came up in game tonight. Thunderwave is a spell with Range: Self (15-foot cube). The description reads:
A wave of thunderous force sweeps out from you. Each creature in a 15-foot cube originating from you...
Players Handbook, 282-283
Does the area of effect center on the caster (extending 7.5 feet in each direction), or does it begin from the caster, and extend in the direction desired (for a full 15 feet)?
No. It is not necessarily centered on the caster (though it can be).
A cube is not a burst power (to borrow a 4e term). The origination point of the cube is anywhere on a face, not necessarily the center. The term face when referring to a cube means the entire square comprising a side.
So you could feasibly center it on yourself, or place yourself in any other point of the cube's effect (and no, you don't have to attack yourself unless you want to).
I wanted to map this out real quick, just so we're all clear. Let's assume we have a 15' cube spell, and let's also use a grid just so we have a bit of clarity, and a limited set of points to operate from. There are 18 possible origin points for a 15' cube, representing two different 3x3 areas (the top and bottom face of a cube). For both of these the graph is the same, but the results are different. If you select the top face, the spell targets the 8 squares in your plane, and the 18 immediately below you. If you choose the origin as the bottom of the cube, then it targets the 8 in your plane and the 18 above you. Now which square is the origin:
XXX
XXX
XXX
Basically, you can be standing in any of the squares that are X and have the burst be those 9 squares. Let's look at a few more examples (Caster is C):
XCX
XXX
XXX
Here you step to a side and have it radiate to your left, right and two rows forward of you.
XXX
XCX
XXX
Here you center it on yourself.
CXX
XXX
XXX
Here you take a corner of the spell and cast it to your left and forward, and radiates out. It seems you should be able to be outside teh area too:
CXXX
XXX
XXX
Since you're adjacent (and heck that could be the middle of a face or the bottom or the top of it. (See the caveat below, this particular form falls much more into the "point" point of origin argument and may or may not be valid in all games.
CAVEAT: There are at least two camps developing around the term "point of origin" used in the text, and depending on which system you came from you may immediately interpret that differently. I have used in this response the version of the term influenced by my 4e experience, which infers that the point of origin is an entire square (this makes a ton of sense when you play with gridded combat as the default, which I do in my 5e games). However, there is a camp that comes from a different point of view that interprets "point of origin" as a singlular point (with an undefined diameter, likely just the part of the cast casting the spell...not sure, I'll let them speak for themselves). This POV would have the caster included in the spell if you cast in the ways that I describe above where the caster is fully within the Xs.
It's important to note that right now both of these interpretations are equally valid and subject to DM interpretation. I'll be using the "point is a whole space unless you don't want it to be" version, feel free to use whichever is most useful in your game (just be consistent about it).
Jeremy Crawford says so. But he only had 140 characters, so let's explain a bit.
Thunderwave has a range of "Self (15-foot cube)"
So we look at "Range":
Spells that create [areas of effect] that originate from you also have a range of self, indicating that the origin point of the spell's effect must be you. (PHB p.202, emphasis mine.)
And then look at "Areas of Effect":
Cube You select a cube's point of origin, which lies anywhere on a face of the cubic effect.... A cube's point of origin is not included in the cube's area of effect, unless you decide otherwise. (PHB p.204, emphasis mine.)
So the origin's on the caster. If you live in the world of squares, let's say the origin's either in the caster's square or on the edge of it. And the origin is on a face of the cube, so the caster is on a face of the cube. You can get arrangements like:
CXXX CXX XXX XXX
XXX XXX CXXX CXX
XXX XXX XXX XXX (and all the rotational variants)
but not
XXX
XCX
XXX
Then one part of your anatomy can be on the face while another part is at the center of the cube.
CC
CCX CCXX CCXX
CCX CCXX XXX
XXX XXX XXX
I disagree that you can center Thunderwave on yourself. The point of origin is on a face of the cube. You could make that point somewhere on the top or bottom, but then the caster's body is included within the cube (only the point of origin can be included or excluded -- the caster's entire body is not the point of origin unless the caster's entire body is on a face of the cube.)
Actually, based on the description on page 205 of the PHB you could have it radiate from you, but you would be included in the effect if you are trying to catch those around you. You are the point of origin and the cube must be attached to you from a cube facing position. Imagine, therefore, that you have the spell emanate from the bottom of your feet up. This would mean you made a decision to include yourself in the area of affect. You will note they do not specifically say "direction" therefore the direction for which the spell goes could include yourself, and would indeed include yourself if the desired effect is to catch all those around you in the effect.
From the PHB Page 205:
You select a cube’s point of origin, which lies anywhere on a face of the cubic effect. The cube’s size is expressed as the length of each side. A cube’s point of origin is not included in the cube’s area of effect, unless you decide otherwise.
It is that,"Unless you decide otherwise.", that informs the option of you centered in the effect. Your point of origin could exist either within or outside the cube, but if you chose to be within you will have decided to be within the area of effect.
For use on a grid (i.e. ignoring verticality), there are only three possibilities:
CXXX
XXX
XXX
XXX
CXXX
XXX
XXX
XXX
CXXX
The origin of the cast is not affected, as stated on p. 204 of the Player's Handbook. Caster can be in the middle of the cube and not take damage.
The description of the thunderwave spell says:
A wave of thunderous force sweeps out from you.
Think Gandalf in the Goblin King Den. Everyone, including his party, was knocked to the ground and he stood unaffected.
Imagine it like this and you can see why being in the center doesn't work: you put out your hand and thunderwave comes into being as a vertical 15x15 square of energy (your hand does not need to be centered on it but must touch it). Then that square moves 15', potentially shoving those in the cube area it has now covered. it's a wave that affects a cube area, not itself a cube.
