Maxperson
Morkus from Orkus
Initiative is called for by the DM, not the player. The player waits for his turn and can then take an action. At no time is he ever invoking initiative. That is done once at the beginning of the fight by the DM.As @pemerton pointed to:
Choosing a target is just picking who you want to attack. It might or might not happen and is subject to action of "I want to attack the ogre." Once the player states his action in response to the DM describing the environment, the mechanics flow from there. The player doesn't invoke the choose a target rule. He's forced to choose a target in order to complete his declared attack.
They aren't invoking the rule. They are subject to the combat rules that were invoked when the DM called for initiative. They have to declare an action, even if that action is sit there and do nothing. Those actions are rules that the player are subject to, not rules that the player is invoking.These rules read that the player gets a turn and when they do they can invoke an action (say Attack) and with an Attack action they make one melee or ranged attack. They then
They players get choices of mechanics, yes, but they do not invoke any of them. The rules make them choose those mechanics due to the combat invoked by the DM when he invoked the combat rules by instructing the players to roll for initative.The combat section is written with a high-degree of mechanical agency for players. @AbdulAlhazred over generalizes in reaching their conclusions. And seeing as parts of the text tells players to invoke rules (choose an action in combat) it isn't right to say that they cannot. As @AbdulAlhazred points out, DM is empowered in the text to override, alter or even ignore anything PCs invoke, but I would not put that in terms of valency. It's laid out that the emerging narrative is intended to have a valency to player invocations and actions. Just as how things go is intended to have a valency with the core book text. DM's supported most in following that, but endorsed to do as they like.