In linguistics, singulative number and collective number (abbreviated and ) are terms used when the grammatical number for multiple items is the unmarked form of a noun, and the noun is specially marked to indicate a single item. This is the opposite of the more common singular–plural pattern, where a noun is unmarked when it represents one item, and is marked to represent more than one item. In some cases, a further distinction is made between the collective and what is known in some terminologies as the plurative, the former referencing multiple items as a class, the latter referencing them as individual units. 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. Welsh has two systems of grammatical number, singular–plural and collective–singulative. 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". Other nouns take the singulative suffixes -yn (for masculine nouns) or -en (for feminine nouns). 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"). When translating the Welsh collective noun into English the plural is usually used, e.g. mefus → 'strawberries'.