# My reading on Rules as Written

The rules are, as you observed, unclear about it, which leaves us with... **Up to the DM**. Now, from how I read/understand it:

**Everything on the readied action must have been decided the moment you readied it.** In particular for your example, "I attack" is not a (complete) action; "I attack the goblin" or "I attack the Bugbear" are (as long as other details, such as "with which weapon?" can be deduced from the context, e.g. the person is only holding one weapon - otherwise these details also should be specified). This is backed by the reading

>Then, you choose the action you will take in response to that trigger

and

>When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger.

Note that **nowhere it states that you can make any change or add any detail to the action** you are taking when the trigger happens - or when you take your reaction. You either take the action you described earlier (without any modification to it) or you ignore the trigger. From how I understand it, that means you can't simply change your action from "I attack" to "I attack the Bugbear" mid-way.

The main point here is: **you can not add any further detail for the action after you have described it when taking the Ready action.** Or, at least, there is no rule that allows it explicitly, thus my reading is that it is not allowed.

Comments suggested that the "If the goblin steps next to me, I move away." example from the book needs more clarification, so clarification should be possible to be made during the reaction. First, I disagree with the premise - given (any) context, this action seems pretty clear for me. Second, I wouldn't try to extrapolate an example for a more general ruling, specifically one with arguably more mechanical impacts than what the example provided.

For explaining better this reading, the intention for the ready action seems to be to delay an action that you could take in your own turn. If you simply said "I attack" as an action in your turn, your DM would simply ask "**Who?**" and "**With which weapon that you are holding?**". If you say "I get ready to attack", I would ask the same questions.

# Extrapolating Crawford's words

When answering about *the trigger*, [Crawford states][1] (thanks [Isaac Reefman][2] for this one)
>Ready action: the trigger should make your intent clear. If you say, "I attack the first enemy I see," only one enemy will qualify. 

While we should be careful on extrapolating tweets from Crawford, assuming the same applies for the *action*, i.e., **the action should make your intent clear** as well, seems fair enough for me. 

-----------

For the Cast a Spell rule you mention, it is a specific rule for the spell case. It does not set and should not be used to set a precedent for the general rule. [I have made the same mistake before][3]. But for that case, you need to specify the spell slot and the target, as when you ready the spell, you are already casting it (reason you lose the spell slot even if the trigger doesn't happen), you simply are not **releasing** it yet. Spells require the target for you to **cast** them, not to **release** them.


  [1]: https://twitter.com/JeremyECrawford/status/861684935278551040
  [2]: https://rpg.stackexchange.com/users/43956/isaac-reefman
  [3]: https://rpg.stackexchange.com/q/123507/43856