On most of the butter knives I’ve seen, the back of the knife is some beveling that almost looks like it’s another blade. But of course it isn’t sharp at all and the beveling is only on one side so the edge is actually quite a lot thicker than the normal “blade”.
Is that just decoration or is there some purpose? You can kind of see it on this picture here.
ETA: On further review, it seems that maybe I’m not talking about a technical 'butter knife" but just rather the knife in a standard silverware set.
I held off hoping another doper had a real answer, but since none has appeared, here is my WAG:
On a knife to be used for stabbing, the back is often ground as pictured in order to make the point sharper. My WAG is that this is done on some table cutlery as a nod to more utilitarian knives.
Knife spines are sometimes beveled to make the blade look thinner without sacrificing strength.
A back bevel might also improve release of cut food from the blade, but I can’t see how that’d apply to a butter knife.
