The mixing of readings from different manuscript traditions or exemplars within a single witness so that the witness preserves a composite set of variants rather than a single, genealogically coherent text.

Principle

When a copyist or editor draws on more than one exemplar for the same passage, the resulting witness cannot be treated as belonging to a single branch of transmission without reading-level analysis.

Demonstration

Illustrative scenario → A medieval scribe copies a passage using two exemplar manuscripts A and B; for some clauses the scribe follows A, for others B, producing manuscript C with a mixture of A- and B-readings. Recognition of C as contaminated leads an editor to evaluate each disputed passage by reference to A and B rather than assuming C represents a single ancestor.

Misapplication

Treating a contaminated witness as a single coherent representative of one tradition and using it uncritically to reconstruct an 'original' reading. The error is to conflate witness-level identity with reading-level plurality.

Consequence

Contamination undermines simple stemmatic models, requires collation at the level of individual readings, and increases reliance on comparative methods and internal criteria to determine earlier forms.

Reversal

If contamination is systematic (for example, a deliberate recension) or confined to marginal readings, the witness may still be useful for reconstructing the text provided the editor identifies and models the pattern of mixture rather than discarding the witness wholesale.

Boundary

Clearly within: a manuscript whose variants align with two distinct manuscript families across different loci. Boundary case: a witness showing occasional assimilation to an exemplar but otherwise coherent. Clearly outside: isolated errors or orthographic differences that do not reflect use of multiple exemplars.

Semantic Tension

Tension between stemmatic purity (treating witnesses as discrete branches) and eclectic methods that evaluate readings individually; contamination forces a choice between genealogical and local reading analyses.

Synthesis

Contamination converts witnesses from unitary nodes in a transmission tree into composite repositories of readings; editors must therefore treat many witnesses as assemblages of local textual histories rather than single ancestral texts.