CLRNC CONFUSION. ARPT CHART VERY CLR AND SPECIFIC.

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BE90 ACFT WAS LOCATED AT THE RAMP AT LOGAN INTL ARPT. WE WERE ADVISED BY GND CTL TO TAXI TO THE BRAVO HOLD POINT (WHILE DEPARTING). NO DEP RWY WAS SPECIFIED. UPON REACHING THE TXWY B HOLD POINT; AN X AIRLINES MD-80 WAS HOLDING TO OUR L. WE HEARD GND ADVISE X TO HOLD FOR THE KING AIR. MY FO ADVISED ME TO CONTINUE TAXIING ON TXWY B BECAUSE X WAS HOLDING FOR US. AS WE CONTINUED; GND MADE US STOP AND COMPLETE A 180 DEG TURN BACK TO THE HOLD POINT. WE WERE BOTH UNSURE AS TO EXACTLY WHERE THE HOLD POINT WAS. AFTER COMPLETING THE 180 DEG TURN; WE WERE ISSUED INSTRUCTIONS TO TAXI TO RWY 4L VIA TXWY B. NO CONFLICT WITH TFC OCCURRED AT ANY TIME. I FEEL THIS PROB AROSE DUE TO SEVERAL FACTORS: A DEP RWY WAS NOT GIVEN. WE ASSUMED RWY 09 WOULD BE OUR DEP RWY BECAUSE THAT WAS STATED IN THE ATIS. IF WE WOULD HAVE KNOWN THAT RWY 4L WOULD BE USED; WE WOULD HAVE REALIZED THAT A R TURN ON TXWY B WOULD BE WRONG. WE ASSUMED THAT X AIRLINES WAS HOLDING FOR US. WE SHOULD HAVE CONFIRMED WITH GND. MY FO CONVINCED ME THAT WE WERE SAFE TO CONTINUE. I THINK MORE SPECIFIC INSTRUCTIONS (STATING A DEP RWY) WHEN TAXIING AT LARGE ARPTS WOULD HELP SOLVE PROBS LIKE THESE. I ALSO THINK FLCS ARE SOMEWHAT AFRAID TO QUESTION INSTRUCTIONS WHEN UNSURE.