Strength Saves resist physical force & restraint. Example: Entangle, gust of wind, thunderwave.
Dexterity Saves resist things where dodging, ducking, or diving can help. Example: Fireball, dart traps, pit traps.
Constitution Saves resist poison, dismemberment, pain, and illness. Example: Lightning bolt, stinking cloud, stunning fist.
Intelligence Saves resist illusions. Example: Phantasmal force.
Wisdom Saves resist madness, strong emotions, and confusion. Example: Cause fear, confusion, feeblemind.
Charisma Saves resist charms, compulsions, and effects that try to make you follow orders, rather than simply feel a certain way. Example: Charm person, dominate monster, suggestion.
I'm pretty well sold on this association of stats-to-saves (though not on the damage side of the equation).
I think I'm a fan of the general notion of active-vs.-passive scenarios for different ability checks mentioned earlier in the thread too. In particular, I think it sorts out the Int/Wis issue as it pertains to Spotting / Searching / Hiding scenarios.
Neither stat governs a character's physical sensory attributes. Being deaf and blind does not modify you Wisdom or Intelligence score, but they ruin your
physical perception.
I'd argue that Intelligence and Wisdom both reflect different means of
processing what your senses tell you - types of discernment. Wisdom is the most likely candidate for passive discernment, while Intelligence is better suited for active scrutiny of a specific object, area, or person. Both depend on input, though. They kick in after the stimulus. If someone is under the effects of both Silence and Invisibility you can't spot them or hear naturally unless they interact with their environment is ways that create perceivable reactions (like footprints in dust, opening a closed door, etc.) - it doesn't matter how high you Wisdom or Intelligence go.
So assuming that there
is some stimulus reaching the character in question that they are capable of sensing, then picking up on what it means is a matter of a Wisdom check if you are unaware or otherwise occupied and Intelligence if you are actively searching for whatever is hidden.
I'd rather leave the physical end of perception to attributes, feats, backgrounds, etc. - things like "Keen Senses," "Sharp-eyed," "Hard of Hearing," etc. These provide guidelines to DMs to decide that while a half-deaf gnome alchemist (too many close proximity explosions) gets no roll to hear something, his human friend might check at Disadvantage and the elf with Keen Senses would roll normally.
I'm also partial to the idea of things like optional feats that allow you to fight off some failed-save-suckage effects out-of-stat as an action. Perhaps calling upon your prodigious physicial strength or strength of will / ego to fight through pain (normally Con) or madness (normally Wisdom), or perhaps using an esoteric mental exercise (Intelligence) to block out your emotions (normally Wisdom) or rationalize away a self-defeating compulsion (normally Charisma). These off-type secondary / substitute saving throws would be special abilities specific to characters (gained via feats, class levels, etc.), not the general rules for effects.
That way "Save vs. Wisdom," or "Save vs. Strength" don't have to cover or exclude every edge case imaginable for every character - just the "normal" ones.
- Marty Lund