Can a spell be cast while using a bonus action to control another spell?

Question

Spells such as the cleric's Spiritual Weapon and the Wizard's Bigby's Hand enable the caster to continue to manipulate the spell's effect as a bonus action after the spell has initially been cast.

Separately, page 203 of the player's handbook states:

Bonus Action A spell cast with a bonus action is especially swift. You must use a bonus action on your turn to cast the spell, provided that you haven’t already taken a bonus action this turn. You can’t cast another spell during the same turn, except for a cantrip with a casting time of 1 action.

Hence my question is does this prohibition apply only to the initial turn on which such a spell is cast, or to all subsequent turns on which the effect is manipulated as well? Put more fully, after casting a spell with a continuing effect manipulated via their bonus action, can a caster use their action to cast a spell (beyond a cantrip) whilst also using their bonus action to manipulate the continuing effect?

Answer 1

Controlling a spell is not casting it

On the first turn, you are right, you can cast Spiritual Weapon (as a bonus action) and a Cantrip (as an action) but not any other spell.

On the subsequent turns you can cast any spell as an action and then use your bonus action to control an already existing spell. In fact, you can have both active and control one of them using your bonus action, while the other one is on standby and still cast another spell.

Note, that Bigby's Hand duration is based on Concentration. This means you will not be able to cast any other Concentration spells if you want to keep Bigby's Hand active at the same time. Spiritual Weapon does not suffer from it.

Answer 2

The text on page 203 is referring to a spell cast as a bonus action. If you cast a spell as a bonus action you cannot cast another spell that turn even if you have remaining actions. Except certain cantrips, of course.

Continuing to manipulate an existing spell effect with a bonus action isn't addressed at all and I would rule isn't covered by the One Spell per Turn restriction. You aren't casting a spell at that point. You are taking an action on something that has already been cast.

So, unless there are other restrictions based on some other situation that applies, you can manipulate an existing effect with a Bonus Action and then cast another spell as well. Assuming you have the requisite actions available to do so.

Answer 3

In subsequent turns, the other spell is not being cast; it is being concentrated on. You are using your bonus action to do whatever it is the spell says you can do; you are not casting a 1 Bonus Action spell. Therefore, you are free to cast another spell with your action or even use the bonus action to cast a bonus action spell and your action to cast a cantrip - obviously, you will not be able to manipulate the concentration spell effect, you only have 1 bonus action.