Only half of us are able to read (4)
I believe the answer is:
scan
'read' is the definition.
(scanning is a kind of reading)
'only half of us are able' is the wordplay.
'only half of' indicates taking half.
'are able' becomes 'can'.
'us' halved is 's'.
's'+'can'='SCAN'
'to' is the link.
(Other definitions for scan that I've seen before include "Glance negligently at" , "Cast an eye over" , "short survey" , "Read electronically" , "Examine data" .)