So here's what we know:
The new counterspell requires the target to be seen, and they must be casting a spell with Verbal, Somatic, or Material components within 60 feet.
Now the key is this. A reaction has a specific trigger....but there is no clause that says that trigger has to be "identified" or "discerned". If the trigger occurs, the reaction can occur. This interpretation is the crux of the debate.
If you go with my interpretation for the trigger....than it doesn't matter if the counterspeller can discern anything about the target's casting. there is no identification of spellcasting whatsoever. Its a simple checklist:
- Are they casting a spell a verbal, somatic, or material components?
- Are they within 60 feet?
- Can I see the target?
If the answer to those 3 is yes....than you counterspell. Its that simple.
What MaxPerson is really digging in is the notion that a reaction trigger has to be "figured out". That its meer happening is not enough, that the person with the reaction has to be able to "discern" that trigger through some method in order for the reaction to occur. That's a reasonable interpretation but I don't know if you could call it RAW.