SMT BEGAN TKOF WITHOUT CLRNC; REALIZED MISTAKE AND TKOF ABORTED.

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REQUESTED TAXI CLRNC AND WAS CLRED TO TAXI TO 36R HOLD SHORT OF J ON PARALLEL TXWY. PRIOR TO REACHING J; A LIGHT SINGLE ENG ACFT TAXIED W TO E ON J AND GND CLRED US TO CROSS RWY 9/27 AND CONTACT TWR. IMMEDIATELY AFTER CALL TO TWR; WE WERE CLRED 'ON TO HOLD RWY 36R.' FO READ BACK 'ON TO HOLD 36R' AND LEFT FREQ TO BRIEF PAX FOR DEP (1 MIN). ON FO RETURN TO INTERCOM; CAPT CALLED FOR LINE-UP CHK AND INITIATED ITEMS NORMALLY HELD UNTIL FINAL TKOF CLRNC RECEIVED. TKOF ROLL INITIATED. TWR ISSUED ADVISORY CALL 'XXX; EXPECT ANOTHER 15-20 SECONDS.' REALIZING TKOF CLRNC WAS IN QUESTION; WE ABORTED AND EXITED RWY AT LL; CONTACTED TWR AND GAVE POS AND STATED WE BELIEVED WE HAD BEEN GIVEN CLRNC FOR TKOF. CTLR DENIED ISSUING CLRNC AND SAID TAPES WOULD BE CHKED. IN RETROSPECT; WE DID NOT NOW BELIEVE CLRNC FOR TKOF HAD BEEN ISSUED. CAPT (PF) MISUNDERSTOOD ORIGINAL TKOF CLRNC AND FO ASSUMED CLRNC WAS ISSUED WHILE OFF FREQ. FACTORS BEARING ON INCIDENT: 'TKOF POS AND HOLD' CLRNC WAS ISSUED WELL BEFORE NORMAL (AT LEAST 3000 FT FROM TKOF POS). WX WAS MARGINAL -- AT OR NEAR FIELD MINIMUMS. CREW WAS OPERATING ON REDUCED REST. THIRD FLT OF 5 SCHEDULED. PREVIOUS ARR AT TPA MISSED APCH ON FIRST ATTEMPT. ACFT NOT EQUIPPED WITH AUTOPLT; MUST BE HAND FLOWN CONTINUALLY. NO FLT ATTENDANT -- FO MUST COMPLETE PRE-DEP BRIEF FOR PAX. OFF FREQ AT KEY PHASE OF FLT. HUMAN ERROR ON PART OF CAPT AND FO. CAPT MISINTERPRETED CLRNC AND FO ASSUMED CLRNC ISSUED. CORRECTIVE ACTION: NEVER ASSUME ANYTHING! WORK TOWARD REVISED FAR ON REST REQUIRED AND EXTENSIVE 'ON TO HOLD' CLRNCS. DOUBLECHK EVERYTHING WHEN TIRED AND THE WX IS DOWN.