My group is pretty new to D&D 5e, and the bonus action is confusing one of our players.
When a monk does an attack from a readied action, can he then use his bonus-action unarmed strike?
I assume he cannot do the bonus attack because it is only usable on when the Attack action is taken, but his argument is that the readied action is the Attack action so it can be used.
During their turn a character can perform:
When a player announces Ready action, they don't delay the whole turn, but only the action:
First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it.
That means you can't do bonus actions via the Ready action, since you only can perform a bonus action on your turn. Moreover, you spend your reaction as well:
When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger. Remember that you can take only one reaction per round.
See the related question: How does the Ready action work in D&D 5e?
The Martial Arts description explicitly says you make the bonus action on your turn:
Martial Arts
When you use the Attack action with an unarmed strike or a monk weapon on your turn, you can make one unarmed strike as a bonus action.
The Ready action (Sage-Advice Compendium)
If you want to wait to act in response to something, take the Ready action, which lets you take part of your turn later
Ready Action (PHB pg. 177)
you can take the Ready action on your turn so that you can act later in the round using your reaction. First, you decide what perceivable circumstance will trigger your reaction.
The Ready action allows you to declare a specific instance, and wait for it to happen in order to use your reaction later in the round.
A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else’s.
Because you are taking the ready action, you are using your turn to wait until someone else's turn in order to trigger said reaction. The ready action would not be considered your turn, because you used your turn to take the ready action, and you are now waiting until later to use the action that was prepared on your turn.
In response to a seperate question in the Sage-Advice Compendium, the answer simply stated:
No, since you can’t take a bonus action on someone else’s turn.
Because the Ready action requires you to wait until someone else's turn, be it enemy, friendly, or even environmental, it is not considered "your turn" and you cannot use a bonus action because of this.
Martial Arts (PHB pg. 72)
When you use the Attack action with an unarmed strike or a monk weapon on your turn, you can make one unarmed strike as a bonus action.
This states that it must be "your turn" to add this bonus action, which you cannot take. Additionally, it also requires you take the Attack action in the first place, which you are not as you are taking the Ready action to prepare an attack, which is not the same as taking the Attack action.
