I am re-reading Ringworld now, and I came across this term; does anyone know where I can find the origin in Niven's canon of work?

1 Answer 1


A reaction drive is a weapon effective in proportion to it's efficiency.

The in-universe origin can be traced back to the first contact between Humans and Kzin where

the drive on the Angel's Pencil (a laser propelled slowboat) is used to destroy a Kzinti warship despite the Kzinti telepath's assessment that the Humans have "no weapons".

(told in "The Warriors") and the subsequent Kzinti attempts to invade the solar system.

Just now I'm not positive about where the phrase first appeared in text, but the Ringworld mention has to be close to the first.

  • According to Wikipedia (en.wikipedia.org/wiki/Man-Kzin_Wars#The_stories) it first appeared in If magazine in 1966. It's probably easiest to find in The Man-Kzin Wars (the first book of short stories).
    – Martha F.
    Commented Mar 14, 2012 at 0:04
  • @MarthaF. I presume that "it" is "The Warriors"? An oddity of copyright law results in the collection not giving that data, but by concern was when the phrase "the Kzinti lesson" first appears. Commented Mar 14, 2012 at 1:45
  • While the Kzinti Lesson isn't mentioned by name (or even paraphrased) in "The Warriors", it shows up in the 1970 novel Ringworld: "A reaction drive is a weapon, powerful in direct ratio to its efficiency." (p.87, first ed. HC, 1977) However, I wouldn't be at all surprised if it were mentioned in the Beowulf Schaeffer stories since the character was prone to chattiness about factoids like this. (1966-1967, 1975) Commented Mar 14, 2012 at 1:49
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    Warning: Do not click on this TV Tropes link. Weaponized Exhaust Commented Mar 14, 2012 at 1:58
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    @Adamant The set-up relies on two things. Firstly that the Kzin use reactionless drives for all stages of space-flight (so no practical experience with mitiigating the risks of drive reaction plumes) and secondly that their telepaths assure them that these prey are disarmed by choice. Commented Jul 22, 2019 at 2:04

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