Simple group contribution methods which incorporate nonadditive, nonconstitutive properties are proposed to predict normal boiling points and melting points for aliphatic, non-hydrogen-bonding compounds. Boiling points and melting points are estimated from the ratio of the enthalpy of transition and the entropy of transition. The enthalpy of transition is assumed to be equal to the summation of group values. The entropy of boiling is estimated using a modification of Trouton’s rule, while the entropy of melting is estimated using a modification of Walden’s rule. The root mean square errors for the estimation of boiling points and melting points are 14.4 K and 34.3 K, respectively.