Sciency Words: Ad Hoc Hypothesis

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Today’s post is part of a special series here on Planet Pailly called Sciency Words. Every Friday, 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” 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?

2 thoughts on “Sciency Words: Ad Hoc Hypothesis

  1. Technically, I don’t think something is a scientific hypothesis if it can’t be tested. However, I suppose a hypothesis could be testable, but not feasible to test. You could say “my hypothesis is testable, all you have to do is move Venus 1/3 AU closer to the sun, crash ten thousand comets into it, and then measure the ratio of nitrogen isotopes.”

    Liked by 1 person

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