Thanks. In my defence, I had checked the definition of 'principal' and found 'something of principal or chief importance' [1] so had thought it was the correct

Thanks. In my defence, I had checked the definition of 'principal' and found 'something of principal or chief importance' [1] so had thought it was the correct option. [1] http://dictionary.reference.com/browse/principal http://dictionary.reference.com/browse/principal