What ability modifier do ray spells use?

Question

My players and I are unsure what ability modifier ranged and melee touch attacks from spells use to hit. Typically, ranged attacks use Dexterity, and melee attacks use Strength. However, spells also have the concept of Spell Rolls, which use the key mental ability for the class.

The Spell Attack section of the Core Rulebook states:

Your proficiency modifier for a spell’s attack roll is the same as your proficiency modifier with spell rolls...Melee touch attacks have the finesse trait.

From these two sentences I inferred that a Spell Attack Roll is different than a Spell Roll. Specifically, the finesse trait would have no meaning if a mental ability score were to be used. However, my players argue that ranged and melee touch attacks are some of the only uses of the spell roll, and it doesn't specifically state that spell attacks don't use the casting ability score.

Are there any rules we're missing or examples of spell attacks that indicate which of these is correct?

Answer 1

Unless redefined by the specific spell, a spell ranged attack uses your Dexterity Modifier

The OP seems to have missed the most significant part of the spell attack rules from p197, just prior to the piece quoted in the question -

Usually, such spells require a melee touch attack or a ranged touch attack. In both cases, make an attack roll and compare the result to the target’s TAC.

The portion quoted by the OP defines a change to the proficiency modifier used, but nothing changes anything else about how a ranged touch attack is resolved. The following from p17 defines how to make attacks.

For modifiers to ranged Strikes, add your character’s proficiency modifier with her weapon plus her Dexterity modifier, plus any item bonus from her weapon and any other bonuses and penalties that always apply.

Note that some specific spells might change this default. The first example I could think of was Spiritual Weapon, on p259, which contains the text

Attacks with the weapon use your attack modifier with that type of weapon, but substitute your spellcasting ability modifier instead of the normal ability modifier.

Note that a Spiritual Weapon doesn't actually make Ranged attacks, but this at least shows how some spells could change the modifier used.

Answer 2

When you "inferred that a Spell Attack Roll is different than a Spell Roll" you were incorrect.

All ranged spells, especially ray spells, are entirely mental and the accuracy of the spell depends on nothing except the caster's ability to visualize the spell striking the target. They do not have any sort of physical requirement beyond whatever somatic components are listed in the spell description. Compare that to a bow and arrow, where the accuracy depends on the archer's ability to hold the arrow in the correct physical alignment so that the arrow is launched on the exact trajectory needed to hit the target.

Touch spells have the finesse modifier for the simple reason that they involve (and require) physically touching the target with your hand. Visualizing the attack is not enough, the caster must make actual physical contact. This physical connection between caster and target means that it makes sense to allow using a physical attribute for the attack roll.