If you write different resonating
structures of aniline,  you will find that aniline is a resonance
hybrid of the following five structures On the other hand, anilinium ion obtained by accepting a proton
can have only two resonating structures (kekule) We know that greater the number of resonating structures, greater
is the stability Thus you can infer that aniline (five resonating
structures) is more stable than anilinium ion