A new interpretation of Lachmann’s Law

In Latin, a short vowel followed by a voiced plosive undergoes lengthening in the past participle (Lachmann’s law). Many of these ppp. show a nasal segment inherited from the present or perfect stem. In a few ppp. moving from a dental stem, such as pēnsus, spōnsus etc., such a spreading provides the condition for the formation of the cluster ns- (< *-nd-þ-to). By observing the supposed omission of -n- in some of these verbal forms (e.g.: frēsus vs. frĕndo), regardless of the effective status of the process, as opposed to its retention in other ones (e.g.: pēnsus vs. pĕndeo/pĕndo), Latin speakers could have hypothesized that all ppp. forms of this group were originally provided with -n-, see e.g. frēsus< *frĕnsus, with loss of -n- and compensatory lengthening of the preceding vowel. The ‘NS-lengthening’ rule might represent an early trigger of the vowel lengthening described by Lachmann. Such a lengthening analogically spread to other ppp., according to a connectionist lexical process.