An idea that I got from Colin Runciman. When marking student work, and you come across a bad answer, ask yourself “is this blank-equivalent, i.e. does this show the same level of insight into the problem as if the student had written nothing?”. In many cases, the answer is “no”. We frequently fail to use points on the marking scale that are between zero and pass, particularly when marking short answer questions in exams. Thinking about “blank equivalence” gives us a tool to decide which answers genuinely show insufficient knowledge or skill to be worth any marks, from those that are still fails, but nonetheless show some insight.
Perhaps the idea of “blank-equivalence” is valuable elsewhere. Perhaps a work of art is not good enough to be worthy of critical attention and positive aesthetic judgement—but, it is still not sufficiently devoid of skill and imagination to make the same impact on the world as doing nothing.