Can you solve this logical-thinking puzzle?

Picture of Saturn
Image: NASA/JPL/Space Science Institute

For anyone locked down and in need of some mental exercise, here’s a quick Japanese challenge. If you only speak English, the puzzle is impossible to solve. If, however, you speak Spanish — or one of a number of other languages, including French, Welsh or Hindi — it becomes an exercise in logical thinking. (The answer is at the bottom of this page, in a piece I wrote about the recent TESOL-SPAIN English-teaching convention at the University of Salamanca.)


In Japanese, the names of the five planets that can be seen with the naked eye are:

  • Mercury – suisei
  • Venus – kinsei
  • Mars – kasei
  • Jupiter – mokusei
  • Saturn – dosei

If the Japanese word for Tuesday is kayoubi, what is the word for Friday?

Is it (a) suiyoubi, (b) kinyoubi, (c) mokuyoubi, or (d) doyoubi?


The link between science and language
Graham Jones | TESOL-SPAIN newsletter (April 2020)

The theme of this year’s TESOL-SPAIN convention was “Breaking barriers”. As an English teacher with a background in astrophysics, my least favourite barrier within education is the one between science and the humanities. The two areas are more deeply intertwined than we often appreciate.

For instance, in his opening plenary in Salamanca, Lindsay Clandfield pointed out that our ideas about robots mostly come from science fiction (step forward C-3PO et al). Significantly, this is true even for scientists and engineers: “Many of the things that people in robotics and artificial intelligence do — they’re quite open about saying they are following things that they were obsessed with as younger people through science fiction,” noted Lindsay.

In the same spirit of “Breaking barriers”, before I began my Sunday-morning presentation in Salamanca, I did a warm-up “challenge” to highlight a link between astronomy and language. If you’d like to have a go, here it is…

In Japanese, the names of the five planets that can be seen with the naked eye are: Mercury – suisei; Venus – kinsei; Mars – kasei; Jupiter – mokusei; Saturn – dosei. If the Japanese word for Tuesday is kayoubi, what is the word for Friday? Is it (a) suiyoubi, (b) kinyoubi, (c) mokuyoubi, or (d) doyoubi?

If you only speak English, the puzzle is impossible to solve. If, however, you speak Spanish, it becomes an exercise in logical thinking. Tuesday (kayoubi) is related to Mars (kasei) in the same way that martes is related to Marte; from this we can deduce that Friday is kinyoubi (since viernes is related to Venus).

Answer = (b) kinyoubi

This can be an interesting topic to think about with students. English retains three clear connections between celestial bodies and days of the week: Satur(n)day, Sunday and Mo(o)nday. For the other days, the connections are still there, but they have been hidden beneath a layer of Germanic influence. For example, Tuesday comes from the Norse god Tiw, who is associated with Mars. Spanish, meanwhile, has lost two connections: sábado comes from the Sabbath (not Saturn), while domingo comes from Dominica (the Lord’s Day).

Published by Graham Jones

Astrophysicist and language teacher