This paper addresses the question of whether pronominal clitics are encoded either in syntax, as minor lexical categories, or in morphology, as inflectional affixes. We examine French varieties, Standard Italian, European Portuguese and Friulian. We propose a violable constraint, the Feature Realization Constraint (FRC). According to the FRC, a feature whose realization is required by some paradigm must always be realized, regardless of contextual conditions. We hypothesize that, in the languages examined, clitic pronominals may violate this constraint, while inflectional affixes do not. Testing this hypothesis against Subject and Object clitics confirms the classic distinction between clitics and affixes. We conclude that there is no empirical justification for locating the items classically considered as clitics in morphology rather than in syntax.