phonological rule
... that in the English plural, the letter -s is pronounced differently in words like "cats", "cabs", and "buses", because of a phonological rule?
... that in the <a class="mw-redirect" href="./English_plural" id="mwECc" rel="mw:WikiLink" title="English plural">English plural</a>, the letter <i id="mwECg">-s</i> is pronounced differently in words like "cats", "cabs", and "buses", because of a <b id="mwECk"><a href="./Phonological_rule" id="mwECo" rel="mw:WikiLink" title="Phonological rule">phonological rule</a></b>?