The diagnostic role of metrical structure is confirmed by the correlation between foot structure and stress with class-specific patterns of inflection, as the old third declension partitive plurals 'algusi and 'endisi give way to new second declension forms 'alguseid and 'endiseid.
This overlap may also help to explain why nouns like PUU are the only second declension nouns that allow partitive plurals in -sid as an alternative to the class-appropriate form in -id.
In principle, akut could be the partitive singular of a second declension noun (on the pattern of motet in table 15) but only if it were the weak counterpart of a strong genitive singular with an initial Q3 syllable.
A similar relation holds between the genitive and nominative singular of open-class second declension nouns, with a couple of qualifications.
Other patterns are of diagnostic value in the first and second declension.
The observation that genitive singulars of most first declension nouns have an even number of syllables while those of second declension nouns often have an odd number of syllables is sometimes taken as evidence that the partitive and genitive plural exhibit syllable-conditioned allomorphy.
Second declension monosyllables like PUU illustrate the first type of case.
The ending -ja identifies each of these as second declension nouns, even though it does not determine a uniform structure.
The contrast between the first declension partitive singular and genitive plural forms 'lippu and 'lippude and the second declension counterparts 'aastat and 'aastate cannot be attributed to any prosodic difference between the stems 'lippu and 'aasta.