Today we tackle fourth hand openers and it involves one of those "Rules." This is (ready?) "The Rule of 15." Now, none of us is going to live long enough to learn all those "rules," and frankly, there isn't enough room left in my memory banks for more. BUT!! Once you understand the concept behind it, you'll not have to struggle...it will just make sense.
When you are in fourth seat, with three Passes in front of you, you have control of the forward action. Since three people have passed, it only stands to reason that the points are fairly even around the table (unless you've got a monster...story for another day). So, if you bid, it will be like the Little Dutch Boy in the story who pulled his thumb out of the hole in the dike and the flood began. Once you bid, everyone will be in the action.
So, under what conditions should you pull out the cork? There are two factors that "rule" your choice: #1: Do you have enough points and/or shape for a rebid? #2: Do you have control of the Spades, God's own suit?
With enough points for a rebid, you can still control the auction. With enough Spades, they have to crawl to the two-level to get involved. And remember, they already passed.
So--with that preparation, here's "The Rule of 15"... Add your High Card Points to the number of Spades you hold. If the total is 15-plus, open. Otherwise PASS PASS PASS PASS. Do you see how this rule of thumb supports the concept of "enough points for a rebid, or control of the Spades?" Easy, peasy. Let's practice!