Where we are requires some clear thought (5)
I believe the answer is:
earth
'where we are' is the definition.
'some clear thought' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'EARTH' is hidden in the letters of 'clear thought'.
'requires' acts as a link.
(Other definitions for earth that I've seen before include "Fox's burrow" , "Heart (anag)" , "Soil; planet" , "wire" , "Fox's or badger's lair" .)