Taking its lead from Walter Bauer's classical work Rechtgläubigkeit und Ketzerei im ältesten Christentum, this paper proposes that the specifically Christian concept of 'heresy' (αἵρεσις) developed from early Christian notions relating to a range of essentially undifferentiated forms of socio-religious evils (κακά/χαλεπά). The modern conception of heresy, in the sense of an unorthodox corruption of true faith in Christ, is clearly recognisable in Christian texts from the late second century onwards. However, when turning to the earliest extant Christian literary sources, one encounters evidence of a way of conceiving of social and religious evil, in which objects of moral and doctrinal concern are judged equally with regard to their disruptive force. It is hypothesised that this way of blurring the distinction between different socially and religiously disruptive dogmas ('proto-heresies') and habits ('proto-sins') may be conceived of as characteristic of a pre-normative religious order. A close reading of the original Greek and Latin text of the Letter to the Philippians – an early second-century work traditionally ascribed to the Christian martyr Polycarp of Smyrna – forms the textual basis against which the theory of the origins of heresy is weighed.