Which spells can be cast across Pathfinder's Wall of Force?

Question

The Wall of Force spell description says, "Breath weapons and spells cannot pass through a wall of force in either direction". But what exactly does this mean ? Specifically,

• Can I cast a Fireball through the Wall of Force ? I'm guessing not, since Fireball creates a projectile that cannot pass the Wall.
• How about a ray spell, such as Scorching Ray ? Again, intuitively, the answer would seem to be "No".
• What about Summon Monster ? Can I sit on one side of the wall, and summon creatures on the other side ?
• In general, what about grid-targeted spells that do not explicitly launch a projectile like Fireball does ?

Answer 1

All of this is about lines (of effect and of sight)

By default, every spell or ability requires line of effect to something to affect that something.

Some of those things require line of sight to that something, and this requirement may be either in addition to, or - in rare cases - without also requiring line of effect.

The thing is, it is always stated if line of effect isn't required for some specific ability or whatever else. As well as there is stated an alternate method of determining, if you may use mentioned ability on something.

In the case of a Wall of Force, you have line of sight, but not line of effect to the other side of it.

All regular effects are incapable of going through the wall, targetted or not (every one of your examples is in this category). Effects like gaze attacks, which specifically say they require line of sight only, work normally, but there are not many of them.

There also are special things like teleport (it targets what should be teleported). So, check individual descriptions carefully. You probably may include spreads here. They can't penetrate barriers but they can circumvent them (they turn corners). So it may affect something behind the Wall of Force relative to its point of origin, provided its area is big enough.