The PHB (p. 144) says:
If you wear armor that you lack proficiency with, you have
disadvantage on any ability check, saving throw, or attack roll that
involves Strength or Dexterity, and you can’t cast spells.
How am I supposed to parse this, as
"If you wear armor with which you lack proficiency, you have disadvantage on
(a) any ability check involving any ability,
(b) any saving throw involving any ability,
(c) any attack roll specifically involving Strength or Dexterity, and
(d) you can't cast spells."
OR as
"If you wear armor with which you lack proficiency, you have disadvantage on
(a) any ability check involving Strength or Dexterity,
(b) any saving throw involving Strength or Dexterity,
(c) any attack roll involving Strength or Dexterity, and
(d) you can't cast spells."
Further, how am I supposed to know which interpretation is correct?
Am I expected to correlate it with other information in the PHB, or is there a standard way to parse grammar when it is vague (for example, always assume ellipses in coordination when possible).
Best Answer
The sentence is, very technically, ambiguous. But it's perfectly clear what is meant
An example of a sentence with the same construction that is similarly technically ambiguous:
Technically it's possible I love all cats and dogs, but for fish, they must also sing. I, personally, would never read it like this.
The rules state
If they wanted to word it differently, they would have done so, something like this:
They did not word it like this, so we do not interpret it like that. On some extremely theoretical level, this sentence is ambiguous. But the construction where the Str/Dex requirement applies solely to attack rolls is so difficult to get out of this sentence that I cannot imagine they even possibly intended it.
Furthermore, as Play Patrice's answer shows, we can determine what the intent was simply by what this rule is meant to do: mechanically implement the lack of mobility that comes from wearing armor one does not know how to wear.