Porson's Law

Porson's Law, or Porson's Bridge, is a metrical law that applies to iambic trimeter, the main spoken metre of Greek tragedy. It does not apply to iambic trimeter in Greek comedy. It was formulated by Richard Porson in his critical edition of Euripides' Hecuba in 1802.

The law states that if a non-monosyllabic word ends on the 9th element of an iambic trimeter, the 9th element must be a short syllable.

A line of iambic trimeter runs as follows:

In this scheme, there are three anceps syllables, marked by the symbol x. These may be long or short.

Porson's Law states that, if the third anceps (i.e. the bolded x above) is long and followed by a word break, then it must be a monosyllable.

A simpler summary of the Law is provided in W. W. Goodwin's Greek Grammar:

M. L. West states it slightly differently, to take account of a rare situation not accounted for by Porson, where the word-break is followed rather than preceded by a monosyllable (e.g. Euripides, Heraclidae 529):

These formulations avoid the difficulty that the reference to the ninth syllable would be inaccurate if there is resolution earlier in he line.

There are, as West observes, very few breaches of Porson's Law in extant Greek tragedy. When the manuscript tradition, therefore, transmits a line that breaches Porson's Law, this is taken as a reason for suspecting that it may be corrupt.

For example, the first line of Euripides' Ion, as transmitted in the mediaeval manuscript Laurentianus 32.2 (known as "L"), the main source for the play, reads:

As Porson himself had already observed in his note on line 347 in his first (1797) edition of Euripides' Hecuba, this line is irregular, since -τοις in νώτοις is long, occurs at the third anceps, and is followed by word break; it therefore breaks the law which Porson later formulated, and it is unlikely that Euripides wrote it as it stands. That the manuscript tradition is incorrect happens to be confirmed by a quotation of this line in a fragmentary papyrus of Philodemus. Philodemus' exact original text is uncertain, but it is reconstructed by Denys Page to read ὁ χαλκέοισι οὐρανὸν νώτοις Ἄτλας (meaning the same as L's version), which does not break Porson's Law, and therefore may be the correct text. However, other scholars have suggested various other possibilities as to what Euripides may originally have written.

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