Should casters and half-casters be able to use a dagger as a bonus action after casting a spell? I had a player tell another player after they cast a spell that is basically their turn. I questioned it, I investigated it and it doesn't make sense that his bonus action disappeared. So, I'm pretty sure my player is wrong.
The relevant weapon property is Light, not Finesse, for using your Bonus Action to make an additional attack. And no, you cannot make an off-hand attack after casting a spell; casting any spell uses the Cast Spell Action, and for Two Weapon Fighting to become available, a player needs to take the Attack Action. Even if they used one of the Sword Coast/Tasha's blade cantrips, they still couldn't use their Bonus Action for a Two Weapon Fighting attack because they'd still have taken the Cast Spell Action, even though the spell in question then makes a Melee Weapon Attack roll.
You only have a bonus action if some class feature or such gives you a bonus action. The only default one is two weapon fighting, which requires you to be holding two weapons (which can complicate spellcasting), and to use the Attack action first. Most things that give bonus action attacks require you to use the Attack action first.
Off the top of my head, the only ways you can do a bonus action weapon attack after casting a spell with your action are:
Eldritch Knight, level 7: War Magic. (bonus action weapon attack after using your action to cast a cantrip)
Valor Bard, level 14: Battle Magic. (bonus action weapon attack after using your action to cast a spell)
Bladesinger Wizard, level 6: Extra Attack. A bit of a roundabout method. Bladesinger's extra attack lets you cast a cantrip as part of the Attack action. If you're holding two weapons, you could then use two weapon fighting to get the a bonus action attack.
Note that it is possible to cast a spell with your Bonus Action and then make your attack(s) with the Attack Action.
Obviously this limits the spells you can cast to spells that have a casting time of a Bonus Action. But there are many spells designed for caster/martial hybrids that have a Bonus Action casting time. Hex, Hunter's Mark, Ensnaring Strike, Banishing Smite, Holy Weapon, Shillelagh, etc.
Should casters and half-casters be able to use a dagger as a bonus action after casting a spell? I had a player tell another player after they cast a spell that is basically their turn. I questioned it, I investigated it and it doesn't make sense that his bonus action disappeared. So, I'm pretty sure my player is wrong.
The relevant weapon property is Light, not Finesse, for using your Bonus Action to make an additional attack. And no, you cannot make an off-hand attack after casting a spell; casting any spell uses the Cast Spell Action, and for Two Weapon Fighting to become available, a player needs to take the Attack Action. Even if they used one of the Sword Coast/Tasha's blade cantrips, they still couldn't use their Bonus Action for a Two Weapon Fighting attack because they'd still have taken the Cast Spell Action, even though the spell in question then makes a Melee Weapon Attack roll.
You only have a bonus action if some class feature or such gives you a bonus action. The only default one is two weapon fighting, which requires you to be holding two weapons (which can complicate spellcasting), and to use the Attack action first. Most things that give bonus action attacks require you to use the Attack action first.
Off the top of my head, the only ways you can do a bonus action weapon attack after casting a spell with your action are:
Well, you always have a Bonus Action, but it's only used when a feature or rule specifically says something uses it.
Note that it is possible to cast a spell with your Bonus Action and then make your attack(s) with the Attack Action.
Obviously this limits the spells you can cast to spells that have a casting time of a Bonus Action. But there are many spells designed for caster/martial hybrids that have a Bonus Action casting time. Hex, Hunter's Mark, Ensnaring Strike, Banishing Smite, Holy Weapon, Shillelagh, etc.
Another way you can attack as a bonus action after casting a spell as an action is with a Scimitar of Speed.