The West-European languages all develop an indefinite article by a grammaticalisation process of the numeral 'one'. The article describes the different outcomes of this process by distinguishing different patterns resulting from the interpretation of the numeral as a quantifier, a classifier or both. The different patterns are examined in their connection and interaction with both the lexical make-up of nouns (homogenous vs. heterogenous nouns) and the category of number (singular, plural and collective) in Germanic and Romance languages. Three different systems are identified: a quantifier system in Germanic, a qualifier system in Modern French and a mixed system in Old French and Spanish