Classifying

Classifying means grouping things by a property they share.

A library groups books by subject. A shop groups items by type. Your phone groups photos by date, place and face. In each case someone chose a property — subject, type, date — and sorted by it.

The property you pick changes everything about the result.

Take five objects: a football, an orange, a book, a cricket ball, a notebook.

Sort by shape: round (football, orange, cricket ball) and flat (book, notebook). Sort by what it's for: sport (football, cricket ball), eating (orange), studying (book, notebook). Sort by can you eat it: yes (orange), no (everything else).

Same five objects. Three completely different groupings. None is wrong — they answer different questions.