Let your "yes" be yes.

James 5:12 (ESV)
But above all, my brothers, do not swear, either by heaven or by earth or by any other oath, but let your "yes" be yes and your "no" be no, so that you may not fall under condemnation.
Swearing, people get that mixed up with cussing these days, and sometimes cursing. There is a difference, and the difference ought to be maintained so that people recognize a sin for a sin. Today it seems you can swear all you want and no one takes notice of it. But use scatological language and heads turn. They can say “God damn it” (which is cursing, not swearing or cussing) all day long on prime time television. To me that seems a little worse than referring to a lousy day as being skubola. But for the sake of more innocent ears I won’t translate that Pauline term for works righteousness.
Swearing is the taking of an oath. Most often this sin is committed when you start a phrase saying “I swear to…” you can swear on your grandmothers grave if you are so inclined. You can swear to God. You can swear on your own good name. You can, but you probably ought not. Back in the day it was considered Christian to let your “yes” be yes and your “no” be no. It was considered insulting that someone should require of you a promise or an oath. A man’s word was his word. If he said he was going to do something he did it. If not, then he meant that too. There was no reason to swear an oath in the name of God to defend the little tidbit of Gossip you were throwing about. Why should you have to swear on that, the fact that you are gossiping has already diluted the integrity of your word. Flippantly swearing to God isn’t going to redeem it.
Now there are times when swearing is permitted, indeed required. Marriage is honored with an oath, commonly referred to as a vow. Both parties make these vows in a wedding, and though they are no longer legally binding, a Christian should recognize that they are making them before God. But that hardly matters to most any more. The think they are vowing to be in love. No, you are vowing to love. There is a difference. Emotions are so fickle as to be unworthy of a vow. But loving is different. You can love, even when you are not in love.
The other time is Military Service. There the country is investing a man with great responsibility, it is right that the man vow to uphold this duty. And it is a duty. No one has the right to go to basic training and learn to kill, destroy and capture other people and property. It isn’t a right. But sometimes one has a duty to do so. I think now might be one of those times, especially if you “have a pair” as we used to say, but find yourself playing Nintendo in your parent’s basement and are over the age of 18. You do realize that currently you have women fighting your battles, right? They are doing that because somewhere along the way, this duty became a right they now have. Doesn’t make sense to me. How is military service a right? I digress. This duty is honored with an oath. If you aren’t man enough to take that oath there, then I don’t want you fighting next to my son when he comes of age.
You might also take an oath, or swear when you take the stand in a court of law to testify. Other than that don’t confuse swearing with cussing, and let your “yes” be yes, and your “no” be no.