I am working thru the LRB and got a little caught up on the conditional chapter. Any tips on how to always get the
sufficient and necessary straight 100% of the time other than memorize every preceding indicator?
Think about all the possibilities.
I'm not going to the movies unless it's raining.
Well, there are four things you might know:
I'm at the movies.
I'm not at the movies.
It's not raining.
Look at each of those, and look again at the statement.
What do you know if I'm at the movies? Well, since I won't go to the movies unless it's raining, if you see me at the movies, it must be the case that it was raining. Thus:
Movies -> Raining
What do you know if I'm not at the movies? Well, the rule says I won't go to the movies unless it's raining, but it doesn't say that I HAVE to go to the movies if it rains, so I don't know anything if I'm not at the movies.
You can always reason these things out and word them into if/then statements and diagram them easily. Just think through the possibilities and play them against the meaning of the conditional statement.
Eventually it becomes second nature.