The practitioner may, then, be (through no fault of his own) out-of-date in his perception of what are the going theories on hos work and its conditions. On the other hand, the danger of explaining 'facts' that are no longer the case, of using out-of-date data; or altermatively, of basing himself on generalised or stylised accounts of phenomens which ignore variations of time and place and setting, whereas any practitioner knows that the particularities of thme and place and setting are much the more significant factors in those phenomena