Can I take a second bonus action in place of my action during a round?

[CapnZapp]

The OP did not say that combat had not started. And they have now confirmed that that is not what they meant.

What the OP meant was "I can't use my action to make an useful attack, can I use it to take a bonus action to speed up my pre-combat buffing".

Feel free to insert the word "melee" in front of my statement if it helps you: "...to speed up my pre-melee combat buffing"

 

[CapnZapp]

I think it would foolish in the extreme to say that you couldn't use a "standard action" to perform a "swift action."

The thing is, even if an action is "swift" enough that you can do it while you do something else, it does not necessarily mean it is "swift" in the sense "I can do it in three seconds, so I can do two of them in a round".

Casting healing word could very well take all six seconds of a round, only you are able to talk at the same time you bash in a kobold's brains. If you don't have any kobolds around, you can't talk twice as fast, and you can't talk with your hands. Why the bashing is an action and the talking "just" a bonus action is simply because the Attack action is deemed to have more weight in, be more central to, this system - you're considered to cast healing word while fighting rather than the other way round.

Here balance meets abstraction. In the end, it's perfectly acceptable to just say no. It's certainly not the case that "realistically" you "should" be able to use your action for a (second) bonus action.

tl;dr: Rule as you wish. Just don't pretend one ruling is more right than the other.

 

[jaelis]

Interesting. It would not have occurred to me that one could cast hex "out of combat", since I would have considered casting hex to be in the same class of actions as shooting an arrow at someone, that is, if something else hadn't already started combat, that would certainly do it. OTOH there certainly are spells that are at least potentially detrimental, such as charm person, that I would not assume initiate combat. I guess I hadn't thought very hard about where to draw the line.

I guess if you assume that the target of spells like hex and bestow curse does not know they are being debuffed, then maybe they would not initiate combat.

Is there a rule or Sage Advice on this that I have overlooked?

The PHB says that generally you don’t automatically know when you are targeted by a spell, unless there are explicit perceptible effects.

To wit:
"Unless a spell has a perceptible effect, a creature might not know it was targeted by a spell at all. An effect like crackling lightning is obvious, but a more subtle effect, such as an attempt to read a creature’s thoughts, typically goes unnoticed, unless a spell says otherwise."