It's probably too early to say whether the doubts being expressed about Social Investment Bonds (SIBs) are fatal or not, but one thing is clear: at best the bonds will function like performance related contracts. An improvement on most current government approaches, perhaps, but in terms of ambition and potential for real change SIBs fall far short of Social Policy Bonds. They aren't tradeable, which sounds like a mere technical detail but in fact severely limits how useful they can be. I've outlined why here, so in this post I'll just concede that Social Impact Bonds is a better name than Social Policy Bonds.
I'm reminded about why I chose the name Social Policy Bonds by the website linked to in the first link, above. It's a long pdf, which documented the meeting at which I first pubicly presented the bond concept, in 1988. I'd originally used the name Social Objective Bonds, until a colleague read my draft paper and told me exactly what
the acronym meant and how widespread it was.