Greenberg's linguistic universal #35 states that no language is purely singulative-collective in the sense that plural is always the null morpheme and singular is not.
Since the loss of the noun inflection system of earlier Celtic, plurals have become unpredictable and can be formed in several ways: by adding a suffix to the end of the word (most commonly -au), as in tad "father" and tadau "fathers", through vowel affection, as in bachgen "boy" and bechgyn "boys", or through a combination of the two, as in chwaer "sister" and chwiorydd "sisters".
Most nouns which inflect according to this system designate objects that are frequently found in groups, for example adar "birds/flock of birds", aderyn "bird"; mefus "a bed of strawberries", mefusen "a strawberry"; plant "children", plentyn "a child"; and coed "forest", coeden "a tree".
Still other nouns use suffixes for both singular and plural forms (e.g. merlen "a pony", merlod "ponies", the unsuffixed *merl does not exist); these are similar to nouns formed from other categories of words (e.g. cardod "charity" gives rise to cardotyn "a beggar" and cardotwyr "beggars").
It is formed by the suffixes: In some cases, the singulative has a further plural indicating a collection of the singular units, which may be broken or regular.
It is generally the collective form which is used as an adjectival modifier, e.g. cig moch ("pig meat", "pork").