Welsh and Irish are two Celtic languages learners often weigh against each other, and they look like natural rivals: small, historic, both revived by determined communities, both with a reputation for spelling that defeats tourists. People reasonably assume that learning one gets you most of the way to the other.
It does not - and the reasons are a good way into what each language is like.
Cousins, not siblings
The Celtic languages still spoken today split into two branches long ago. Welsh is Brythonic, alongside Breton and Cornish. Irish is Goidelic, alongside Scottish Gaelic and Manx. Irish and Scottish Gaelic are close; Irish and Welsh are not mutually intelligible, and their everyday vocabulary is mostly different.
What they share is architecture. Learn one and the other's grammar will feel oddly familiar, even while its words do not.
What they have in common
The verb comes first. Both are verb-subject-object languages: "Is the weather cold", not "The weather is cold". Our grammar notes for Welsh and Irish both start there, because everything else hangs on it.
Words change at the front. This is the famous one. In both languages, the first sound of a word can change depending on the word before it. Welsh cath (cat) becomes ei gath (his cat), fy nghath (my cat) and ei chath (her cat). Welsh has three of these mutations - soft, nasal and aspirate; Irish has two main ones, lenition and eclipsis. They look chaotic for a few weeks and then turn out to be rule-driven, and they carry real meaning: in Welsh, the mutation is often the only thing that tells "his cat" from "her cat".
Prepositions conjugate. "At me", "on you", "with her" are single inflected words. Irish uses this for possession - tá carr agam, literally "a car is at me" - where English says "I have".
There is no single word for yes. In both languages you usually answer a question by echoing its verb - "Are you?" "Am." - so "yes" and "no" change with the question. It is one of the first things that makes both feel genuinely foreign.
What genuinely differs
Spelling. Welsh spelling is consistent once you learn its conventions, which are simply different from English: w and y can be vowels, dd is the "th" in "this", f is a "v" and ff an "f", and ll is a sound English does not have. Irish spelling is also rule-governed, but its rules take longer to absorb: consonant clusters that mark lenition and eclipsis, and a system in which vowels around a consonant signal how the consonant is pronounced. Bhfuil is pronounced roughly "will". Most learners find Welsh easier to read aloud early on.
Mutations, in the detail. Irish marks its mutations visibly in the spelling - an h after the first consonant for lenition, a new letter in front for eclipsis - which helps once you know what to look for. Welsh mutations replace the letter outright, so you have to learn to un-mutate a word to find it in the dictionary. The soft mutation is the one you will meet first and most.
Where you will hear it. In the 2021 census, about 18 percent of people in Wales aged three and over reported that they could speak Welsh, and it is widely visible in public life there - signs, schools, broadcasting. Irish is the first official language of Ireland and taught in its schools, but daily use outside education is concentrated in the Gaeltacht, the Irish-speaking regions, and in urban networks of speakers; Ireland's census shows many more people reporting that they can speak Irish than reporting that they use it every day.
Dialects. Both have them. Irish has three main dialect areas - Munster, Connacht and Ulster - with a written standard across them, and the differences in pronunciation are large enough that learners often pick one. Welsh has a well-known north/south divide in everyday vocabulary and some grammar.
How to choose
As with any pair, the structural comparison is close to a tie, so it will not decide for you. Our Irish vs Welsh page shows that directly: a near-identical course size, the same verb-system shape, and one clear difference, which is audio.
What will decide it:
- Family, place or heritage. Most people learning either language have a
reason with a name attached - a grandparent, a move, a school a child attends. That reason will keep you going through the mutations.
- Access to the sound. A minority language lives in its speakers, and
hearing it is half the work. If you can get to Welsh-language radio, television or a local class more easily than Irish, that is a real advantage.
- If you are genuinely undecided, Welsh's spelling usually makes the
first months smoother.
Learning them on Semantix
Both run the full A1-to-C1 path - 18 units each, a checkpoint at the end of every unit, and grammar notes in plain English that explain mutations before the drills that practise them.
The one real difference is audio, and we would rather tell you up front: Welsh has a text-to-speech voice (a standard voice, not one of the more natural neural ones), so you can hear tutor replies and cards. Irish has no voice from our speech provider, so on Semantix it is text-only. Given how much Irish pronunciation depends on hearing it, we recommend pairing it with Irish-language radio or a class. Speaking practice uses your browser's speech recognition, and whether that recognises Welsh or Irish depends on your browser.
Start from the Welsh or Irish page, or try a conversation in either.