Sciency Words: Ad Hoc Hypothesis

Today’s post is part of a special series that first appeared on Planet Pailly. Every Thursday, we take a look at a new and interesting scientific term to help us all expand our scientific vocabularies together. Today’s word is:

Ad Hoc Hypothesis

“Ad hoc” is a Latin phrase meaning “for this,” as in “for this one and only one purpose.” Within the sciences, the term has rather negative connotations. Basically, it’s technical jargon for “Oh come on! You just made that up!”

A scientific hypothesis can be labeled “ad hoc” if any one of the following conditions are met.

  • The hypothesis attempts to explain one and only one phenomenon.
  • The hypothesis contradicts part or all of our current body of scientific knowledge.
  • The hypothesis cannot be tested in any meaningful way.

The ad-hoc-ness of an ad hoc hypothesis increases when you find any combination of the above conditions. Please remember that ad hoc hypotheses are not necessarily wrong, but in the minds of scientists, they are highly suspect.

You’ll encounter the term ad hoc in many scientific papers as well as in books and articles about science. There’s even an event called BAH-Fest(that’s the Festival of Bad Ad Hoc Hypotheses) where professional scientists compete over who can come up with the most hilarious ad hoc hypothesis.

And yet, the term does not seem to appear very often in science fiction, despite the fact that it fits so well with a common Sci Fi trope: the scientific genius whose radical new theory has not been accepted by his/her peers.

Rejected dialogue from Back to the Future:

Marty McFly: But Doc, your time travel theory falls apart without the ad hoc explanation of the flux capacitor.

Or as a response to meaningless technobabble:

Rejected dialogue from Star Trek:

Ensign Chekov: The ship must have entered some sort of quantum asymmetrical graviton loop singularity!

Commander Spock: Mr. Chekov, kindly refrain from postulating ad hoc theories. We must investigate this phenomenon further.

Or in any discussion involving conspiracy theories:

Rejected dialogue from The X-Files:

Agent Mulder: These crop circles must be part of an elaborate government cover-up.

Agent Scully: Do you have any evidence for that, or is this just another ad hoc hypothesis?

Okay, maybe those aren’t the best examples. So how would you use the term ad hoc in a story?


Written by James Pailly.

To read all the articles in the ‘Sciency Words‘ series, visit the Planet Pailly blog.

  • Leonardo Faria

    I would name Ad Hoc an artificial intelligence specializing in heuristic exploration of off the wall modelling (to the point of ridicule). It would be member of a panel of AIs that brainstorm hypotheses of DNA recombination. The role Ad Hoc would play is to break with its audacity of assumptions the conventionalism of too rigid computing patterns.