stable carbocations are carbocations stabilized by resonance,
in order of stability to lesser stability
tertiary > secondary > primary > methyl
tertiary and secondary carbocations are stabilized by hyperconjugation or the interactions between a sigma bond orbital and a pi anti ponding orbital
basically hyperconjugation is good, so that rules put methyl and primary as terrible
resonance is good, tertiary displas most hyperconjugation and resonance forms.
