Mikael Parsons and Richard I. Pervo challenge this assumption in Rethinking the Unity of Luke and Acts (1993). They draw attention to the differences in genre, narrative, and theology between Luke and Acts and highlight a number of authorial and canonical questions posed by Luke and Acts. At stake is whether we link Luke and Acts with a hyphen (Luke–Acts = a close connection) or with a forward slash (Luke/Acts = a loose connection). Gregory writes:
A second-front against the unity of Luke-Acts has opened up from studies in reception history. Andrew Gregory's book The Reception of Luke and Acts in the Period Before Irenaeus (WUNT, 2.169; Tübingen: Mohr [Siebeck], 2003) argues that Luke and Acts were not read together in the second century with the exception of the Muratorian fragment and Irenaeus. Luke was normally read with the tetraevangelium (four Gospels) and Acts was read in the company of the Apostolos (collection of catholic letters).
Behind this question lies the modern assumption that Luke and Acts are two volumes of one longer work, each of which was written by the same author. Therefore it is important to realise that Luke–Acts as an object of study, two separate texts linked by a hyphen, is in fact a modern construct. Of course this is not to deny that Luke wrote two successive volumes – and perhaps even set out to write two successive volumes – each of which largely coheres with and informs the other. Rather, it is simply to note that for much of their subsequent history Luke’s two volumes have not been read in this way and, consequently, that it is not possible to assume that the knowledge and use of one of these texts by a subsequent reader or text need in itself require or indeed make probable the knowledge and use of the other. Nor do we know if ever they circulated together in this period, for once Luke released each volume he would have had no control over its circulation and copying.I see two primary questions emerging from all this:
(1) Literary critics frequently assume that Luke and Acts were written as part of the one work, but were separated early in the second-century. Is this assumption valid? Does the fact that Luke and Acts were rarely (if ever) read together count against a unity of Luke and Acts?
(2) To what extent do we allow the second and third century authors to inform us of the authorial intention, initial reception, and interpretation of a first century writing? How close is Irenaeus to the mind of Luke and is the absence of evidence the evidence of absence regarding their being read together? How much continuity should we posit between first century and second century readings of these documents?
Such is the topic of my paper at the BNTC later this month.