"The application of the by-law in a particular case is therefore not to be approached through a meticulous examination of the details of processes or activities, or to a precise cataloguing of individual items of goods dealt in, but by asking what, according to ordinary terminology, as the appropriate designation of the purpose being served by the use of the premises at the material date. This question being answered, it remains only to enquire, when a use that is being made of the premises at a later date is challenged is not being authorised by By-law 370, whether that use is really in substantial use for the designated purpose. That will often be a question of fact and degree: ... and for that reason border-line cases will inevitably arise in which opinions will differ. But to seek more precise guidance from the by-laws is vain. The general considerations that have been mentioned will suffice for most cases. If premises were being used as professional offices at the commencement of the by-laws, no greater degree of particularity in defining the purpose is likely to appeal to practical minds is appropriate in the application of town-planning legislation that is involved in saying that the purpose is that of professional offices: the particular profession of the occupant would not ordinarily be adverted to by a person speaking in a town-planning context. The answer is perhaps not so easy in the case of a shop. As to a butcher's shop, for example, I should be inclined to think that while it would be immaterial to enquire into the details of the user the `purpose' in the relevant sense would be the purpose of a butcher's shop and not of a shop generally. In the case of a general store, wide variations in the use as regards the nature of the stock carried and the methods of merchandising might occur before one would say, in an ordinary use of language, that the premises were not being used for the same purpose as before. In the case of premises used for pottery making, however, it seems to me clear that while changes in methods and designs would be immaterial the use of the premises for making anything other than pottery would be, in a substantial and relevant sense, used for a different purpose."