In aliphatic amines, the −NH₂ group is attached to an alkyl group which is an electron donating group i.e, they have +I effect. So, the lone pair of electrons on nitrogen are readily available. In aromatic amines, the −NH₂ group is attached to a −C₆H₅ group, which is an electron withdrawing group. So, the availability of a lone pair of electrons on N is decreased. Therefore aliphatic amines are more basic than aromatic amines.