Polarisation is a term used in cladistics to “refer to the imposition of direction onto character state change or character transformation. A character is said to be polarised when the [ancestral, primitive] state has been distinguished from the apomorphic [derived] state” (Kitching et al. 1998², 48 – see also the glossary, ibidem, p. 213).
In textual criticism, “polarisation” might be used to indicate the same operation amongst variants: i.e. the imposition of direction onto variation. A variant location is said to be polarised when the primary variant (primitive state) has been distinguished from the secondary variant (derived state) (See Robinson and O'Hara 1996). The terms ‘primary / secondary variants’ may be preferred against controversial terms such as ‘error / mistake’ and ‘good / original reading’. This terminology, although not accepted by everyone, indeed offers the advantage of clarity. For instance, a correction could be secondary, but it would be unusual to characterise it as a ‘mistake’. It is also a relative terminology, which implies a judgement about the chronology of the variation, and not about the ‘correctness’ of the variants (although ‘correctness’ is often one of the criteria used to establish this chronology). A primary variant could give way to a secondary variant, which in turn may be seen as the primary variant in a further variation.
In the Maas-Lachmann method, only secondary readings may be used to draw the stemma, as in cladistics, in theory, only an apomorphic state of a given character (i.e. the result of a genetic mutation) indicates the existence of a new clade.
In both fields, textual criticism and evolutionary biology, establishing which is the primitive and which is the derived state has always been a very difficult question, giving rise to many debates (see Robins 2007). Therefore, the possibility of drawing unrooted trees, without any presupposed assumptions about the direction of the variation, but relying on the principle of parsimony, has been welcomed by biologists and by textual scholars (see Robinson and O’Hara 1996, and Robins 2007).
The problem is, however, that in textual criticism an unrooted tree cannot be considered a stemma as information about the direction is needed for many problems. The question therefore remains how to introduce chronology and directionality into the set of variation. This should be, and usually is done by using both external criteria, about the history of the manuscripts (see Robinson and O’Hara 1996), as well as internal criteria in order to polarise some of the variant states. Out-group comparison is another method, unfortunately not always applicable, but very efficient, to orientate a tree.
– Kitching, Ian J., Peter L. Forey, Christopher J. Humphries, and David M. Williams. 1998. Cladistics: The Theory and Practice of Parsimony Analysis. 2nd ed. Oxford: Oxford University Press.
– Robins, William. 2007. “Editing and Evolution.” Literature Compass 4 (1): 89–120.
– Robinson, Peter M. W., and Robert J. O’Hara. 1996. “Cladistic Analysis of an Old Norse Manuscript Tradition.” Research in Humanities Computing 4: 115–137.
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