The phonology of Welsh is characterised by a number of sounds that do not occur in English and are typologically rare in European languages, such as the voiceless lateral fricative [ɬ] and voiceless nasal consonants. Stress usually falls on the penultimate syllable in polysyllabic words, while the word-final unstressed syllable receives a higher pitch than the stressed syllable.
Welsh morphology has much in common with that of the other modern Insular Celtic languages, such as the use of initial consonant mutations, and the use of so-called "conjugated prepositions" (prepositions that fuse with the personal pronouns that are their object). Welsh nouns belong to one of two grammatical genders, masculine and feminine, but are not inflected for case. Welsh has a variety of different endings to indicate the plural, and two endings to indicate the singular of some nouns. In spoken Welsh, verb inflection is indicated primarily by the use of auxiliary verbs, rather than by the inflection of the main verb. In literary Welsh, on the other hand, inflection of the main verb is usual.
The Welsh for "I like Rhodri" is Rydw i'n hoffi Rhodri ("I am liking [of] Rhodri"), but "I like him " is Rydw i'n ei hoffi — literally, "I am his liking him" —; "I like you " is Rydw i'n dy hoffi di ("I am your liking you"), etc.
While English can either use verbs directly (e.g. "I go") or with the aid of an auxiliary verb ("I am going", here using "to be" as the auxiliary), non-literary Welsh inclines very strongly towards the latter use. In the present tense, all verbs are used with the auxiliary bod (to be), so dw i'n mynd is literally "I am going", but also means simply "I go". In the past and future tenses, there are inflected forms of all verbs (which are invariably used in the written language), but it is more common nowadays in speech to use the verbal noun ( berfenw , loosely equal to the infinitive in English) together with the inflected form of gwneud (to do), so "I went" can be mi es i or mi wnes i fynd and "I will go" can be mi a' i or mi wna i fynd . There is also a future form using the auxiliary bod , giving fydda i'n mynd (perhaps best translated as "I will be going") and an imperfect tense (a continuous/habitual past tense) also using bod , with roeddwn i'n mynd meaning "I used to go/I was going".
Mi or fe is often placed before inflected verbs to show that they are declarative. In the present and imperfect of the verb bod (to be), yr is used instead. Mi is mainly restricted to colloquial Northern Welsh, with fe predominating in the South and in the formal or literary register. Such marking of the declarative is, in any case, rather less common in higher registers.
The traditional counting system used by the Welsh language is vigesimal, which is to say it is based on twenties, as in standard French numbers 70 ( soixante-dix , literally "sixty-ten") through 99 ( quatre-vingt-dix-neuf , literally "four twenties nineteen"). Welsh numbers from 11 through 14 are " x on ten", 16 through 19 are " x on fifteen" (though 18 is more usually "two nines"); numbers from 21 through 39 are "1–19 on twenty", 40 is "two twenties", 60 is "three twenties", etc.
There is also a decimal counting system, which appears to be commonly used in Patagonian Welsh, where numbers are " x ten y ", e.g. thirty-five in decimal is tri deg pump (three ten five) while in vigesimal it is pymtheg ar hugain (fifteen – itself "five-ten" – on twenty).
While there is only one word for "one" ( un ), it triggers Soft Mutation Treiglad Meddal of feminine nouns, other than those beginning with ll and rh. There are separate masculine and feminine forms of the numbers "two" ( dau and dwy ), "three" ( tri and tair ) and "four" ( pedwar and pedair ), which must agree with the grammatical gender of the objects being counted.