In certain constructions, a (sub-)morphological unit may be devoid of any recognizable meaning or function. There are two kinds of submorphemic units:

  1. parts of morphs with a sound-symbolic value (as in glare, glow, glitter etc.)
  2. expression elements inserted between morphs on purely structural (morphological, phonological or even phonetic) conditions.

Type #1 is not generally subjected to morphological analysis and may therefore be foregone here. Type #2 is instantiated by the second element in forms such as French a-t-il ‘has he’ and Germ. Weihnacht-s-gans ‘Christmas goose’. The German interfix -ig in is another case in point. This is otherwise an adjectivizing suffix and would receive the gloss Adjr in other contexts like wolk-ig (cloud-Adjr) ‘cloudy’. In words such as the one of , it is an obligatory interfix mediating the derivation of the abstract noun ‘fastness’ from the adjectival base ‘fast’. There are at least three solutions for such cases:

  1. Assign the seemingly functionless element a function. By the principle ‘same morpheme – same gloss’, one may use the same gloss that the element receives in contexts where it is functional. The result would be as shown in .

    .Schnell-ig-keit
    Germanfast-ADJR-ness
    fastness

    However, this may seem wrong because if the element does have a different function (viz. no function) in this context, it cannot be an allomorph of the same morpheme. Then one may assign it a label of this distinct function. Some put catalytic (affix) (Cat), others put euphonic (element) (Eu).

  2. In converse analogy with case #2c of the zero morphemes, the unit may receive the gloss ∅, as in '.

    '.Schnell-ig-keit
    Germanfast-∅-ness
    fastness

    Rule 9. A (sub-)morphemic unit of L1 with no recognizable linguistic function may be glossed by the zero symbol (∅).

  3. In converse analogy with case #2a of the zero morphemes, one may refrain from individuating such an element in the morphophonemic representation in the first place and simply treat it as part of its host morph.

    ''.Schnellig-keit
    Germanfast-ness
    fastness

    Here schnellig is (certainly inappropriately in this particular case) treated as an allomorph of the morpheme schnell. (Remember that the gloss does not reflect allomorphy.)

Again, the choice among solutions #a – #c is not a matter of proper glossing, but of morphological theory and analysis.