To characterise statistical inference in the workplace this paper compares a prototypical type of statistical inference at work, statistical process control (SPC), with a type of statistical inference that is better known in educational settings, hypothesis testing. Although there are some similarities between the reasoning structure involved in hypothesis testing and SPC that point to key characteristics of statistical inference in general, there are also crucial differences. These come to the fore when we characterise statistical inference within what we call a "space of reasons"--a conglomerate of reasons and implications, evidence and conclusions, causes and effects. (Contains 1 figure.)