Wikipedia:Category escape hatches

A category escape hatch is a parent->subcat relationship involving two completely different branches of science. For example the relationship between Category:Earth and Category:Planets of the Solar System is an escape hatch; it makes Category:Earth (and indirectly all of Wikipedia's geographical content) a subcat (after many levels in between) of Category:Astronomy.

Category escape hatches are generally inappropriate per WP:SUBCAT, as it is rarely the case that the members of the subcategory really can be expected (with possibly a few exceptions) to belong to the parent also. Category escape hatches are also a major contributior to category cycles, if there are two escape hatches that for a loop. For example, prior to Special:Diff/1298171537, we had the following loop:

• Earth -> Planets of the Solar System -> [... non-escape hatch parents in astronomy] -> Outer space -> [Earth sciences: Sky -> Meteorological concepts -> Meteorology -> Physical geography -> Earth sciences -> Earth]

Since there was an escape hatch from earth sciences -> astronomy and another one from astronomy -> earth sciences, we have a loop. And the only way of avoiding that loop is to break one of the bolded arrows.

Another example is Category:Humans; it's tempting to add that to its taxonomic parent Category:Hominina, however that opens an anthropology -> taxonomy escape hatch that would cause a ton of category loops (since almost everything has to do with humans somehow so Category:Humans is very large). Here's one example, with escape hatches in bold, found using https://categorypath.toolforge.org.

Human activities -> Human behavior -> Humans -> Hominina -> [... non-escape hatch parents in taxonomy] -> Animal taxonomy -> Zoological nomenclature -> Biological nomenclature -> Biology terminology -> Terminology -> Language -> Human communication -> Human activities.

Instead, only the article Human should be in that parent. Likewise despite the technical relationship Category:People should not be in Category:Individual apes because it would open an eponymous -> taxonomy escape hatch (a lot of things are named after people, so a lot of content is in Category:People via enough layers).

Sometimes escape hatches are tricky to avoid. For example, it's difficult to imagine how else to parent Category:Earth as being a solar system planet is its one defining relationship. And the precise location of the second bolded hatch is a matter of disupte; it could be where I put it. Or you might call the relationship between Category:Animal taxonomy and Category:Zoological nomenclature the escape hatch, but Taxonomy is the fundamental idea of naming things. Either of those challenges is difficult to sustain.

It's particularly difficult to avoid escape hatches for WP:EPONCATs, which are by definition topic categories, and many of the parents are set categories, but do your best to avoid it.

"Humans" is a common escape hatch target as explained above, since nearly every article touches on humans in some way or another. "Terminology" in another one. Hence, these fields must not themselves escape into even broader topics.