We can make a similar examination, but with greater uncertainty, of the extraterrestrial hypothesis that holds that a wide range of UFOs viewed on the planet Earth are space vehicles from planets of other stars.
Carl Sagan (1973). “Carl Sagan's Cosmic Connection: An Extraterrestrial Perspective”, p.200, Cambridge University Press
![We can make a similar examination, but with greater uncertainty, of the extraterrestrial hypothesis that holds that a wide range of UFOs viewed on the planet Earth are space vehicles from planets of other stars.](http://cdn.quoteddaily.com/images/carl-sagan/we-can-make-a-similar-examination-but-with-greater-uncertainty-of-the-extraterrestrial-hypothesis-that-holds-that-a-wide-range.jpg)