\section*{Appendix--Some Diachronic Issues}
\label{appendix}
Something is known of the historical development of the systems under discussion in this paper, and
that history, we think, sheds additional light on the analytic and theoretical questions that we
have been grappling with. We consider these issues in a summary way in this Appendix. 

For this discussion, we will return to our \textsc{type three} allomorphy (from section \ref{sec:allo}),
which concerns the form of the conditional ending in Northern dialects.  That ending has the
orthographic form -\textit{f(e)adh}.  The availability of that single orthographic form hides from
easy view the striking variation in form that we care about. That alternation is illustrated once
more in \Next: 
\ex.\label{ex:opaque}\a. chuirfeadh Seán \ldots\ \qquad(John would put)\\
         /\textipa{x1r\super{j}hu Sa:n}/
     \b. chuirfeadh sé  \ldots\  \qquad\ \ \ \ (he would put)\\
         /\textipa{x1r\super{j}h1t\super{j}S@}/

\Last[a] shows the default form of the ending; \Last[b] shows the form that emerges in the context of
\spi. The phonological distance between the two forms (/\textipa{hu}/ and -/\textipa{h1t\super{j}}/)
means that this alternation is deeply opaque in the context of the contemporary phonology of Irish
and it is for this reason that we analyze it as an instance of suppletive allomorphy. 

The two forms and their relation are, however, readily understandable in terms of the historical
phonology of the language. The original form of this ending (in the Old Irish period, 600--900) was
something like /\textipa{h@D}/ with a final voiced dental fricative; it is for this reason that the
standard orthographic form is still \textit{dh}.  But the dental fricatives were lost before the
emergence of Early Modern Irish in the first half of the thirteenth century.  They were lost by way
of phonemic merger -- Old Irish /\textipa{G}/ and /\textipa{D}/ merged to /\textipa{G}/.  This
development was complete by the time of the emergence of Early Modern Irish around 1200, but
evidence for it first makes its appearance in the written record -- sporadically -- during the
Middle Irish period---between 900 and 1200 (\citealt[ 234]{breatnach:94}, \citealt[
351]{macmanus:94}) Once this merger had done its work, the conditional ending would have had a form
something like -/\textipa{h@G}/.\footnote{We set aside some complex and unresolved questions about
  whether the initial consonant of the morpheme was originally /\textipa{f}/ or /\textipa{h}/.}

In final unaccented syllables, the sequence /\textipa{@G}/ subsequently develops in different ways
in different dialects. In Ulster (our focus for the moment) the development was as in \Next:
\ex.  /\textipa{@G}/ $\Longrightarrow$ /\textipa{@w}/ $\Longrightarrow$ /\textipa{u:}/ $\Longrightarrow$ /\textipa{u}/

It is by way of this succession of changes that the ending -\textit{f(e)adh} comes to have the form
/\textipa{hu}/ in contemporary Ulster varieties.

The variant /\textipa{h1t\super{j}}/, meanwhile, was stranded, preserving in its contemporary form a
memory of the long lost final dental. The form has its origins in an assimilatory devoicing and
palatalization of final /\textipa{D}/ when immediately followed by, and in close combination
with, the initial /\textipa{S}/ of the third person simple pronouns. So the modern alternation
of \LLast\ has its origins in the older and much more transparent alternation in \Next:
\ex. \a. /\textipa{h@D}/    (default)
     \b. /\textipa{h1t\super{j}}/  when in close combination with a pronoun whose initial is /\textipa{S}/

While the conditional morpheme in its default form still ended
in /\textipa{D}/, the alternation between final /\textipa{@D}/ and final /\textipa{1t\super{j}}/ was
easily analyzed in phonological rather than morphological terms, as an instance of phonological
sandhi. As a consequence of the existence of this sandhi form, in what became the environment for
\spi, the final consonant was protected from the sequence of changes in \LLast\ which led to
emergence of the default form -/\textipa{hu}/. It is in this way that the contemporary alternation
emerges.  

We can understand the historical sequence here by assuming that what was first a prosodic
incorporation of the subject pronoun is later reinterpreted along the lines we have suggested here
for the modern language. That is: as alternations as opaque as those in \ref{ex:opaque} gradually
accumulate, a morphological interpretation of incorporation, as opposed to a phonological or
prosodic interpretation, is forced on learners of the language, since the opaque alternations had to
be analyzed in terms of suppletion rather than as the reflection of a regular or semi-regular
phonological process.

What is now interesting is that these shifts interact with the emergence of pronoun postposing in a
rather striking way.  Independent pronouns first emerge early in the Middle Irish period (900 or
thereabouts) and the possibility of pronoun postposing emerges with them. At this point, we assume,
the evidence available to learners favored a prosodic, rather than a morphological, understanding of
pronoun incorporation. It is one of the more important points of section \ref{sec:spi2} of our paper
that, given a prosodic understanding of incorporation, we expect pronoun postposing to be available
to subject pronouns. This follows from the logic of the analysis developed in \cite{bem-1,bem-2}.
If this is on the right track, we will expect that as long as a phonological understanding of \spi\
remains available, postposing should be available for subject pronouns. As the evidence for
a morphological reinterpretation becomes stronger (as the transparent alternations of \Last\ yield
to the opaque alternations of \ref{ex:opaque}), then the logic of exemption, as laid out in section
\ref{sec:spi2}, should come into play and the modern system (in which postposing is forbidden
to subject pronouns) should emerge.

This is in fact, at least to a first approximation, how things took their course. When postposing
first emerges (with the emergence of independent pronouns) postposing was in fact available to
subject pronouns (\citealt[\ 111]{greene:58}, \citealt[\ 75]{ahlqvist:75}, \citealt[\
272-274]{breatnach:94}):
\exg. arn\={a}ch t\={\i}ssad friss h\={e}.\\
      so-that-not {approach\past\subj\he} against-it he\\
     `so that he would not oppose it'\hfill{\cite[\ 273]{breatnach:94}}

This is exactly the correlation that the logic of our discussion would lead us to expect. 

While much work remains to be done to if these speculations are to be fleshed out (in particular, we
would need more information than is at present available about the detailed chronology of the
relevant changes), we take it to be a strength of our overall analysis that it opens this door to an
understanding of how and why the strange ban on postposing of subjects emerged. The analysis invites
us to make a link between that fact and apparently unrelated facts about the emergence of opaque
allomorphic alternations in inflectional endings.

