Calculations appear to be switched for theologian and scholar (7)
I believe the answer is:
erasmus
'scholar' is the definition.
(I know that Erasmus is a humanist)
'calculations appear to be switched' is the wordplay.
'calculations' becomes 'sums' (I've seen this before).
'appear to be' becomes 'are' (I am not sure about this - if you are sure you should believe this answer much more).
'switched' says the letters should be written backwards.
'sums'+'are'='sumsare'
'sumsare' backwards is 'ERASMUS'.
'for theologian and' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for erasmus that I've seen before include "Fifteenth to sixteenth century Dutch humanist, use arms (anag.)" , "Desiderius -, Dutch scholar, humanist" , "Humanist critical of Church" , "Old theologian" , "religious scholar" .)