“Common elements” could mean “the intersection of two sets” (which is probably what you meant) or “a set of attributes that are correlated with the set of interest” (which is where “most people find church boring” fits).
Generalizing could be a means of abstracting the important elements from a set, or a means of predicting elements to be found in future examples of a set. So, saying “pies are desert,” could mean that a peach pie shares important features with cake (more so than sharing features with a particular shade of off-white paint), or that when a menu says pie the diner can expect it to be sweet and come after the primary meal (even though some pies are savory).
Notes:
“Common elements” could mean “the intersection of two sets” (which is probably what you meant) or “a set of attributes that are correlated with the set of interest” (which is where “most people find church boring” fits).
Generalizing could be a means of abstracting the important elements from a set, or a means of predicting elements to be found in future examples of a set. So, saying “pies are desert,” could mean that a peach pie shares important features with cake (more so than sharing features with a particular shade of off-white paint), or that when a menu says pie the diner can expect it to be sweet and come after the primary meal (even though some pies are savory).