I'm having a minor disagreement with my DM and this seems like a good place to sort it out.
My DM believes that ability score modifier only applies to the first attack a character makes in a round. So a fighter with two attacks would only add their strength modifier to the first attack.
My understanding is the only time you don't add your ability modifier is with your bonus action attack when fighting with two weapons.
You definitely do get your ability score modifier added to the damage of all melee attacks done as part of the Attack action (including any given by Extra Attack). You don't add it to the Bonus Action attack you get from two-weapon fighting, unless you have the Two-Weapon Fighting Style. You do only add the bonus damage once (per attack) for critical hits, though, even though you roll twice the dice.
I'm having a minor disagreement with my DM and this seems like a good place to sort it out.
My DM believes that ability score modifier only applies to the first attack a character makes in a round. So a fighter with two attacks would only add their strength modifier to the first attack.
My understanding is the only time you don't add your ability modifier is with your bonus action attack when fighting with two weapons.
Have I missed something?
You definitely do get your ability score modifier added to the damage of all melee attacks done as part of the Attack action (including any given by Extra Attack). You don't add it to the Bonus Action attack you get from two-weapon fighting, unless you have the Two-Weapon Fighting Style. You do only add the bonus damage once (per attack) for critical hits, though, even though you roll twice the dice.
You are right. There is no rule saying that you can add the damage modifier only once per turn.