The allomorphs of the past tense all have the orthographic form -ed, but phonologically they are [əd], [d], and [t].

The [əd] allomorph follows roots ending in [t] or [d]; the [t] allomorph follows roots ending in voiceless obstruents, and the [d] allomorph follows roots ending in voiced stops and fricatives, liquids, nasals, and vowels.

The underlying or “elsewhere” form is likely to be [d] since it is found after the greatest variety of sounds. In addition, it is easy to derive the other allomorphs from it by natural phonological processed: schwa insertion to break up a cluster of two alveolar stops will yield [əd], and voice assimilation will yield [t].

Note that the rule is read downward. Thus, since [t] and [d] occur in the first line, they are not included among the voiceless consonants in the second line or other sounds in the third line.

These forms are all grammatically rather than phonologically conditioned. Some are realized by a vowel change (sing/sang), some by a vowel change plus an inflectional ending (bring/brought), some by a zero morph (cut/cut), and some by a different form entirely (go/went).

These forms are in free variation.

The allomorphs appear to be il-, ir-, im-, and in-. Note, however, that il- and ir- are both pronounced [ɪ], im- is pronounced [ɪm], in- is pronounced [ɪn] (in intolerant, insecure, infamous, etc.) but [ɪŋ] in ingrate and incongruous.

The [ɪ] allomorph is conditioned by a following liquid (as initial sound of the root), the [ɪm] allomorph by a following bilabial, the [ɪŋ] by a following velar stop, and [ɪn] by a following vowel, or labiodental, alveolar, or alveopalatal consonants.

[ɪn] appears to be the underlying form since it is found in the greatest variety of environments and is the form from which the other forms can be derived most easily: [ɪm] and [ɪŋ] by assimilation in place of articulation to the place of the following sound (with no change in manner of articulation), and [ɪ] by loss of the nasal.

The meaning is ‘not’.

The word ignoble comes from Latin gnōbilis ‘noble’ (which later lost its initial consonant to give nōbilis, hence noble). When in- was combined with gnobilis, the first n dropped out, giving English ignoble. The g is thus part of the root, not part of the prefix. The word ignominious comes from Latin nōmen ‘name’; it acquired a g by mistaken analogy with gnōsco, a process called “contamination”.

Again, the orthography is a bit misleading. The allomorphs seem to be col-, cor-, con-, co-, and com-. However, the phonological forms are actually [kə], [kən], [koʊ], and [kəm] since the [l] in col-, the [r] in cor-, the [n] in con- before the alveolar nasal, and the [m] in com- before the bilabial nasal is actually part of the root.

It is rather difficult to know which is the “elsewhere” form in this case. Historically, the com- [kom] form is original. If it is considered the underlying form, the [kən] form is derived by assimilation in place of articulation to the following stop with vowel reduction, the [kə] form by reduction of the vowel and loss of the [m] before liquids and nasals, and the [koʊ] form by loss of the [m] and vowel shift.

The meaning is either associative ‘with, together’ as in compare, cohabit, coexist, collect, etc., or intensive ‘completely’, as in correct, contend, corrode, etc.

In all of the words, the final syllable in the unsuffixed form is [aɪn] and the same syllable in the suffixed form is [ɪgn].