Sciency Words: CETI vs. SETI

Hello, friends!  Welcome back to Sciency Words, a special series here on Planet Pailly where we take a closer look at the definitions and etymologies of scientific terms.  Today on Sciency Words, we’re talking about:


On October 10, 1966, scientists from the International Academy of Astronautics met in Madrid, Spain, to discuss CETI: Communications with ExtraTerrestrial Intelligence.  This was surely not the first time the term CETI was ever used, but based on my research, that 1966 meeting seems to be the earliest official usage of the term by the scientific community.

CETI refers to the act of sending signals or messages out into space for the express purpose of making contact with intelligent alien life.  It’s the human race shouting into the void, asking if anybody’s out there.  The most famous example of this is the Arecibo message, which was broadcast from the Arecibo radio telescope in Puerto Rico in 1974.

The idea of deliberately trying to attract the attention of extraterrestrials has always been controversial.  What if an alien intelligence does hear us?  What if that alien intelligence is not friendly?  But for the purposes of a Sciency Words post, I’m going to skip over that controversy and focus on the controversy about the word CETI itself.

CETI is far too easily confused with SETI (the Search for ExtraTerrestrial Intelligence).  CETI and SETI are closely related fields, but there’s one very important distinction between them.  It’s the difference between talking and listening.  CETI is about trying to talk to the rest of the civilized universe (assuming other civilizations exist, of course).  SETI is about listening patiently to see if anyone out there is trying to talk to us.

According to Google ngrams, the term CETI peaked in the late 1970’s/early 1980’s.  Since then, the term METI (Messaging ExtraTerrestrial Intelligence) has far surpassed CETI.  And in 2018, a special committee on SETI nomenclature recommended that CETI be dropped from scientific discourse in favor of METI.

And yet CETI still appears, from time to time, in scientific research.  For example, this paper from June of 2020 uses the term CETI extensively.  But we’ll talk about that paper more on Monday.  It makes some rather bold predictions about how many CETI-capable civilizations should exist in our galaxy at this very moment.

P.S.: The authors of that 2020 paper offer another solution to the CETI vs. SETI problem.  They suggest CETI should be pronounced as “chetee.”  I’m not sure how I feel about that.

P.P.S.: Actually, I am sure how I feel about that.  I’d rather use the term METI instead.

9 thoughts on “Sciency Words: CETI vs. SETI

  1. I think I’d assumed, every time I saw CETI, was that it was pronounced keti. If people were walking around pronouncing it the same way as SETI, then it definitely had to go.

    That said, while I think SETI is a long shot, METI seems pointless. We already have an ever expanding sphere of radio communication spreading out from our position.

    Liked by 1 person

    1. I was wondering if anyone did a hard-C sound for CETI. That makes much more sense to me than “chetee.”

      As for our sphere of ever-expanding radio signals, I’ve read conflicting things about that. Supposedly, as radio broadcasts spread farther and farther from Earth, the signal gets weaker, and at some point it’s so weak it just blends in with all the background radiation. People involved in METI say they have to use very high powered radio signals aimed at specific targets. Otherwise, the transmission probably won’t get through.

      Liked by 1 person

    1. Good thing you caught that! I feel like that might be another reason the SETI nomenclature committee wants to drop CETI. There are a whole bunch of stars with Ceti in their names.


    1. Yeah, if only we could communicate via thought-waves, as respectable species do. Still, symbolic communication systems allow us to be creative. There are advantages to that as well.


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