Four statutes, four different jobs

The instrument nearly every animal question in a home turns on. It bars discrimination in the sale and rental of housing and, since the 1988 amendments, requires adjustments to rules where a disabled person needs one to use their home fully.

Its definition of the animal is deliberately wide: it asks whether the animal is needed, not whether it was trained. That single choice is why an animal accepted at home may be turned away everywhere else.

The oldest of the four in this field. It attaches a condition to federal funding: a programme that takes the money may not exclude disabled people from what it offers.

In housing it matters most in subsidised and public developments, where it layers on top of the Fair Housing Act and occasionally reaches situations the newer statute does not.

Aviation sits outside every other regime and always has. Its rules are set by the transport regulator, revised substantially in recent years, and applied by carriers rather than by any building owner.

The current position is narrow: trained dogs travel in the cabin on production of a federal attestation form completed in advance. Animals whose value lies in presence alone are handled under each carrier's ordinary policy for pets.

The instrument that governs entry to shops, restaurants, hotels, surgeries, government buildings and workplaces. Its definition is the narrowest of the four, and deliberately so: a doorway decision has to be made in seconds, without any enquiry into health.

Only dogs qualify, with a separate limited provision for miniature horses, and only where the animal is trained to do something specific. Presence alone does not open a public door.