There are many changes of the final sound or inflexions (infhillteacha) some with various flexion suffixes, e.g. plural suffixes like -tha, -a, -í, -anna, -acha or verb suffixes like -im, -ann, -tar etc. This is known as outward flexion.
This is the case in all inflected languages.
The more importantly described flexions are those in the word stem or word root , which many languages demonstrate. In German these are the phonetic mutation progressions (Ab- and Umlaute) like "lauf, lief, ging, gegangen", etc. One terms this as inner flexion
Those root changes typical in Irish are similar to the German mutations through old, yet often lost suffixes, which once affected the word root (comp. dt. Fuß - Füße, ir. fear - fir [originally: fer - firi])
As opposed to German, in Irish the changes in slenderness of the final consonants are in the foreground and not the vowels (comp. bord - boird [bord - bord'])
Syncopation ist also to be found in German (e.g. wechseln, ich wechsle)

Palatalisation (an Caolú)

This is no more than that a "broad" consonant is replaced with its "slender" component.
Because slender and broad consonants are denoted orthographically by appropriate vowels in their proximity, it follows that:
In written Irish this is mostly noted by an inserted i.

e.g.     bád (a boat) becomes báid (of a boat or boats)
So, the broad d in bád becomes slender d in báid.

Partially there are also certain mutations necessary for the preceding vowels, that then again almost remind one on the German Ablaute and Umlaute:
 

e.g.:    fear (a man) becomes fir (of a man or men)
So, the broad r in fear becomes slender r in fir
Additional vowel mutations (real Ablaute e.g. mac - mic) are more the exception than the rule.

Caolú aids in the formation of

• the genitive and vocative in the 1st declension of nouns (e.g. an fear - an fhir - a fhir)
• the weak plural of the 1st declension of nouns (e.g. an fear - na fir)
• the genitive of the 2nd declension of nouns + suffix -e (e.g. an lámh - na láimhe)
• the (old) dative and the dual of the 2nd declension of nouns (e.g. an lámh - ar an láimh - dhá láimh)
• the genitive of the 1st declension of adjectives, in the feminine form + suffix -e (e.g. fliuch - fliche)

Depalatalisation (an Leathnú)

This means a "slender" consonant is replaced with a "broad" consonant.
(opposite principle of palatalisation)
In written Irish mostly only an i is omitted :

e.g.   abhainn (a river) becomes abhann (of a river)
So, the slender -nn in abhainn becomes broad -nn in abhann

Sometimes more complex mutations need to be taken in the vowels (i zu ea, etc., partially the reverse of palatalisation, s.o.)
 

e.g.: Éirinn (Ireland) becomes Éireann (of Ireland)
so, the slender -nn in Éirinn becomes a broad -nn in Éireann

Leathnú aids in the formation of:

• the genitive of the nouns of the 3rd declension (e.g. mil - meala)
• the genitive of many nouns of the 5th declension (e.g. Éirinn - Éireann)
• the genitive of the adjectives of the 2nd declension (e.g. bródúil - bródúla)
• the form of some verbal nouns (e.g. cuir - cur)

Syncopation (an Coimriú)

Syncopation occurs in bi- and polysyllabic words.
Syncopation means that the vowel of the last syllable of the stem is omitted . (e.g. inis zu insíonn)
So, the originally bisyllabic word stem is shortened and monosyllabic (inis zu ins-)

This always occurs when the following 3 characteristics come together:

1. the vowel of the last syllable is unstressed and without accent
   (e.g. the second i in inis = tell )
2. this vowel is between a liquid (l, m, n, r) and another consonant
   (e.g. n in inis)
3. to such a polysyllabic word an additional conjugation, declension, plural or other suffix is added
   (e.g. inis + suffix -íonn: insíonn)

• Syncopation also leads to a mutation of vowels/consonants in the first syllable, if the rule "Caol le caol" (slender with slender) requires:
  e.g.: ramhar - raimhre, domhain - doimhne
• nn, ll, rr are shortened to l, n, r. e.g. aoibhinn - aoibhne (not: aibhnne)
• If combinations occur through syncopation like ln / nl / dl, then ll is written instead. Instead of dn / nd then nn.
  e.g.: álainn - áille (instead of: áilne) or ólann - ólla (instead of: ólna)
  (The exception in written Irish of a retained -dl-: codail - codladh. The pronunciation of codladh is however [koL@], as if one had written*colladh).

a few important examples:

• preceding conjugation suffixes of syncopating verbs, mostly of the 2nd conjugation ending in -il, -ir, -in, partially also -is (if a l, m, n, r comes in front of it, see above)
  e.g.: cosain - cosnaíonn, imir - imríonn, inis - insíonn, etc.
• in the declination of adjectives : e.g. the feminine genitive suffix -e, plural suffix-a, -e:
  e.g.: an bhean ramhar = the fat woman - na mná raimhre = of the fat woman - na mná ramhra = the fat women

change from voiced to unvoiced (an Díghlórú)

This only occurs before an ending that begins with [h] beginnen. It is especially the future suffixes with f- and verb- and verbal adjective endings with th-.
The voiced consonants b, d, g, bh, mh are devoiced by the [h], which [h] mutes, -bth- is then spoken [p].
Often, even the spelling is simplified since the spelling reform: dth > dt, mhth > f, bhth > f

One should not confuse the consoant cluster -bhf- within a word with the bhf- as an eclipsis of f-. The latter is spoken [v/w].