For example, if there is a bowl of mixed peanuts and raisins, and one desires the raisins and dislikes the peanuts: Removing (effectively sorting) the peanuts from the bowl, leaving a 'purified' pile of raisins free from unwanted peanuts, would be Sorting/purification as the peanuts are removed. However, removing the "desirable" raisins from the peanuts does not purify the mixture, as one is left with undesirable peanuts (hence unrefined) not a refined component as before, and is thus permissible. Note that in this case there has not been any extraction of material from either the peanuts or raisins (threshing/extraction), just the sorting of undesirable from desirable (sorting/purification).