Super-brief sketchy summary for those wondering whether to follow the link (I do wish there were a community norm that people making link posts provide such summaries):

Link is to a blog-post by Benquo, which considers what sort of thing a pledge or promise is, what it does, and how to understand it. (Context: recent discussion among Effective Altruists of the "Giving What We Can" pledge and how strong a commitment it should be understood as.) Proposes that a key way of thinking about a pledge is as a prediction of future behaviour on which others may rely; so when considering whether to make such a pledge you should consider how confidently you can make that prediction.