- this is 100% my own view (and innate ability) except that you DO have to use "which" for non-restrictive clauses, don't attempt "this clause, that is non-restrictive, gets commas," oceans will boil, mountains crumble etc
- People sometimes ask me when to use "that" and when to use "which". Interestingly, there is no known rule for this. Unless you were born with the instinctive ability to tell which one sounds right, like I was, you will simply never know
