Phonological Alternations

Phonological alternations in Sereer are characterized vastly differently depending on the portion of the word they occur in. On the one hand, Sereer has stems that are fairly invariant in size, almost exclusively alternating by way of morphologically determined consonant mutation of initial (or sometimes final) segments. On the other hand, affixes (and especially verbal suffixes) have phonologically determined allomorphs that alternate between the segmental shapes -VC and -C, seemingly motivated by an avoidance of overlong consonant clusters and hiatus. There is a trade-off in phonological content, then, between invariance in terms of shape (in stems, whose segments do change) and invariance in terms of segments (in affixes, whose shape does change).

Stem Morphophonology

Sereer has salient alternations in the initial consonants of noun and verb stems. These alternations appear to be morphologically conditioned in a lexically specified manner, since they occur in several different segmental contexts whose only common element is being within a morphologically derived environment (e.g. plurality in both nouns and verbs; addition of apparent nominalizing suffixes to verbs).

Nouns

(discussion on sg./pl. alternations here)

Deverbal nouns: A noun can be formed from (any?) verb by affixing a prefix a- to the verb root, and altering the initial consonant of the root.

verb	meaning	noun	meaning
ret	go	atet	a trip, "going"
ɗing	fence (in)	aƭing	fence
tos	gather manure	atos	pile of manure
piis	draw a line	apiis	line
weʄ	swim	abeʄ	a swim, swimming

Further alternations remain to be seen, but it appears that the same sorts of alternations seen elsewhere in the language are present here (r,d > t ; voiced implosive > voiceless implosives, etc.)

There are some less straightforward alternations involving not only the initial consonant:

rain (v): deɓ
rain (n): ateƥ

slap (v): faɗ
slap (n): ombaƭ

Verbs

The initial consonant of verb roots can vary based on whether the subject is singular or plural. Non-implosives alternate with prenasalized stops, and implosives alternate with their voiceless counterparts. Alternations are mostly, but not completely, predictable (note multiple possible alternations for /s/ and /q/).

sg.~pl.
f~mb
b~mb
w~mb
ɉ~ɲɉ
χ~ɴɢ
ɗ~ƭ
ɓ~ƥ
ʄ~ƈ
r~nd
d~nd
g~ng

Invariant:
j~j
l~l
m~m
n~n
ŋ~ŋ
ɲ~ɲ
p~p
t~t
k~k
c~c
s~s
ʔ~ʔ

We still need to get the sg vs. pl. forms of verbs starting with:
q

It seems that verb roots (as seen with singular subjects) cannot start with voiceless implosives or prenasalized stops.

Postverbal Affixes

A number of postverbal affixes exhibit a morphophonological alternation between a -VC and -C form. The -VC form appears between consonants, or after a consonant at the end of word, and the -C form appears elsewhere.

1st sg. subject: -(u)m

gef-aa-m 'I break'
vs.
gef-aa-n-um 'I break it'

2nd sg. object: -(o)ng

3rd sg. object: -(i)n

Causative: -(i)n

Reciprocal: -(i)r

Itive: -(i)k

Instrumental applicative: -(i)t

Reversive: -(i)t