What does "inconceivable" mean?

Inconceivable: Not conceivable; incapable of being conceived by the mind; not explicable by the human intellect, or by any known principles or agencies; incomprehensible; as, it is inconceivable to us how the will acts in producing muscular motion. It is inconceivable to me that a spiritual substance should represent an extended figure. Locke. -- In`con*ceiv"a*ble*ness, n. -- In`con*ceiv"a*bly, adv. The inconceivableness of a quality existing without any subject to possess it. A. Tucker.