Each ability partially describes your character and affects some of his or her actions. Creatures have six ability scores that many game mechanics are influenced by.
- Strength (Str) measures your character's muscle and physical power.
- Dexterity (Dex) measures hand-eye coordination, agility, reflexes, and balance.
- Constitution (Con) represents your character's health and stamina.
- Intelligence (Int) determines how well your character learns and reasons.
- Wisdom (Wis) describes a character's willpower, common sense, perception, and intuition.
- Charisma (Cha) measures a character's force of personality, persuasiveness, personal magnetism, ability to lead, and physical attractiveness.
When an ability score changes, all attributes associated with that score (attack bonuses, AC, hit points, etc) change accordingly. However, a character does not retroactively get additional skill points for previous levels if she increases her intelligence. Ability scores are often also referred to as "stats", for historical reasons.
Each ability has a modifier associated with it. Starting out this will usually be in the range of -5 to +5, though ability modifiers above +5 are possible. The table shows ability modifiers up to +6. For ability scores not shown, simply continue the progression: Every 2 full ability points above 10 gives +1 ability modifier.
The modifier is the number you apply to the die roll when your character tries to do something related to that ability. You also use the modifier with some numbers that aren't die rolls. A positive modifier is called a bonus, and a negative modifier is called a penalty.
The ability score linked to a spellcaster's magic is, as one might expect, very important to them. A spellcaster must have an ability score of 10 + the spell's level to cast a spell of that level, and the saving throw DC of a spellcaster's spells is 10 + Spell Level + linked Ability Modifier. Each spellcasting class uses a different ability, usually Int or Cha for an arcane caster and Wis for a divine caster.
Spellcasters also gain bonus spell slots based on their casting stat. For each spell level, 1st through 9th, if your ability modifier is equal to the spell level, you get one bonus spell of that level. For every 4 additional points of modifier that you have over the base amount required you get an extra bonus slot of that level. For example, a spellcaster with a 28 in their casting stat (+9 modifier) would have 3 bonus 1st level slots, 2 bonus slots for levels 2nd through 5th, and 1 bonus slot for levels 6th through 9th. If their casting stat gained two points (+10 mod) they'd get an additional 2nd and 6th level lot.
If a spellcaster doesn't have access to a given spell level that they would get bonus slots for, they can still fill those spell slots with additional 1st level spells 1. For example, Digapoli is a 3rd level wizard with an intelligence of 18. His intelligence gives him a bonus spell slot for each level 1st through 4th. However, because he is only a 3rd level wizard, he can only actually cast 1st and 2nd level spells. His bonus 3rd and 4th level spell slots aren't fully available to him, but he can put 1st level spells into those slots if he wishes. Casters who don't prepare spells can use their additional slots to cast additional 1st level spells as well.
| Stat | Mod | 1st | 2nd | 3rd | 4th | 5th | 6th |
|---|---|---|---|---|---|---|---|
| 1 | -5 | --- | --- | --- | --- | --- | --- |
| 2-3 | -4 | --- | --- | --- | --- | --- | --- |
| 4-5 | -3 | --- | --- | --- | --- | --- | --- |
| 6-7 | -2 | --- | --- | --- | --- | --- | --- |
| 8-9 | -1 | --- | --- | --- | --- | --- | --- |
| 10-11 | +0 | --- | --- | --- | --- | --- | --- |
| 12-13 | +1 | 1 | --- | --- | --- | --- | --- |
| 14-15 | +2 | 1 | 1 | --- | --- | --- | --- |
| 16-17 | +3 | 1 | 1 | 1 | --- | --- | --- |
| 18-19 | +4 | 1 | 1 | 1 | 1 | --- | --- |
| 20-21 | +5 | 2 | 1 | 1 | 1 | 1 | --- |
| 22-23 | +6 | 2 | 2 | 1 | 1 | 1 | 1 |
Footnotes
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This is a somewhat subtle change: In the SRD, a spellcaster doesn't get bonus spell slots at all for a spell level they can't use. However, that just means they almost always run out of spells too soon at lower levels, which is dumb, not fun, and just not magical enough. ↩