Numbers in Irish

In Brief

Irish uses one set of forms for saying numbers by themselves—a haon, a dó, a trí—but normally drops a when counting nouns: dhá chapall (“two horses”). The noun generally stays singular; 2–6 cause lenition (a change marked in many words by adding h) and 7–10 cause eclipsis (a different consonant is written before the original one). People are often counted with special forms such as beirt (“two people”) and triúr (“three people”).

Overview

Numbers are among the first things learned at A1, but Irish does more with them than English does. In English, the number changes while the following noun simply becomes plural: “two horses,” “seven horses.” In Irish, the number can change the noun’s first sound, and the noun after a simple number is normally singular: dhá chapall, literally “two horse,” and seacht gcapall, literally “seven [eclipsed] horse.”

It helps to learn three related systems rather than one long list. First come the independent forms, used when reciting numbers, doing arithmetic, giving a score, or reading a digit. Second are numbers placed directly before a noun. Third are the personal numerals, special words used to count people. The beginner rule is regular enough to use immediately; spelling details and numbers above twenty can then be added in layers.

A noun is a word for a person, place, thing, or idea, such as cat (“cat”), teach (“house”), or bliain (“year”). Mutation means a change to the beginning of such a word. Irish spelling shows these changes, so they matter in both speech and writing.

How It Works

Saying numbers on their own

Use the counting particle a before 1–10 when no noun follows. It changes the beginning of several numbers: a haon, a dó, a trí, a ceathair. The h in haon belongs to this independent counting form; it is not used in aon chat.

Number	Independent form	Approximate use
1	a haon	one
2	a dó	two
3	a trí	three
4	a ceathair	four
5	a cúig	five
6	a sé	six
7	a seacht	seven
8	a hocht	eight
9	a naoi	nine
10	a deich	ten

For example, a phone number can be read digit by digit with these forms. In arithmetic, a dó agus a trí is “two and three.” Do not carry this a over into an ordinary noun phrase: say trí leabhar, not a trí leabhar.

Counting things from one to ten

Put the number directly before the noun. The core pattern is:

Number	Form before a noun	Mutation	Example
1	aon	lenition	aon chat amháin — one cat
2	dhá	lenition	dhá chapall — two horses
3	trí	lenition	trí chat — three cats
4	ceithre	lenition	ceithre theach — four houses
5	cúig	lenition	cúig theach — five houses
6	sé	lenition	sé chat — six cats
7	seacht	eclipsis	seacht gcapall — seven horses
8	ocht	eclipsis	ocht gcapall — eight horses
9	naoi	eclipsis	naoi gcapall — nine horses
10	deich	eclipsis	deich gcapall — ten horses

The noun is shown in its singular form even when the English translation requires a plural. Thus teach remains teach in cúig theach, and capall remains identifiable inside gcapall in seacht gcapall.

With aon, Irish commonly adds amháin after the noun when the meaning is exactly “one” or “only one”: aon chat amháin. In many fixed or indefinite expressions, aon can instead mean “any”: aon lá can mean “any day” or, depending on context, “one day.”

Recognising lenition and eclipsis

Lenition usually inserts h after the first consonant: cat → chat, capall → chapall, teach → theach, bád → bhád. Not every initial letter can be lenited, and some spelling environments block a visible change. Learn the regular pattern first, but copy the form you meet in reliable examples rather than trying to add h mechanically to every word.

Eclipsis places another consonant before the original one. Common written pairs are:

Basic initial	Eclipsed initial	Example after 7–10
b	mb	seacht mbád — seven boats
c	gc	ocht gcat — eight cats
d	nd	naoi ndoras — nine doors
f	bhf	deich bhfuinneog — ten windows
g	ng	seacht ngairdín — seven gardens
p	bp	ocht bpunt — eight pounds
t	dt	deich dteach — ten houses

The spelling keeps the original consonant visible. In gcapall, for instance, c is the first letter of the unmutated word capall.

Eleven to nineteen

Add déag after the unit. In independent counting, the particle remains:

Number	Independent form
11	a haon déag
12	a dó dhéag
13	a trí déag
14	a ceathair déag
15	a cúig déag
16	a sé déag
17	a seacht déag
18	a hocht déag
19	a naoi déag

When a noun is counted, it goes between the unit and déag: trí chat déag (“thirteen cats”), seacht gcapall déag (“seventeen horses”). The mutation is still controlled by the unit number. Notice the special lenited dhéag after dó in the independent form a dó dhéag.

The tens up to one hundred

Number	Irish
20	fiche
30	tríocha
40	daichead
50	caoga
60	seasca
70	seachtó
80	ochtó
90	nócha
100	céad

Modern decimal-style forms place the unit after the ten: fiche a haon (21), tríocha a cúig (35), nócha a naoi (99). You will also meet the traditional pattern with is/agus (“and”), especially with ages, measurements, and established expressions: bliain is fiche (“twenty-one years”) and cúig bliana is fiche (“twenty-five years”). Usage can vary by region, context, and house style, so beginners should first learn to recognise both patterns rather than force every compound number into one formula.

For an exact hundred, céad can stand alone as the number “one hundred.” Before a noun, forms such as céad duine (“one hundred people”) are common.

Counting people

For small groups of people, Irish strongly favors personal numerals. These do not mean “persons” in the abstract; the idea of people is built into the numeral.

Number of people	Personal numeral	Example
1	duine amháin	one person
2	beirt	beirt chairde — two friends
3	triúr	triúr páistí — three children
4	ceathrar	ceathrar múinteoirí — four teachers
5	cúigear	cúigear daltaí — five students
6	seisear	seisear fear — six men
7	seachtar	seachtar ban — seven women
8	ochtar	ochtar imreoirí — eight players
9	naonúr	naonúr cuairteoirí — nine visitors
10	deichniúr	deichniúr oibrithe — ten workers

A noun following a personal numeral is normally in the genitive plural, a form used here to connect the group with the kind of people in it. You do not need to master that form at A1. For now, learn frequent combinations as whole phrases: beirt bhan, triúr fear, ceathrar páistí. Personal numerals can also stand alone when the people are already understood: Bhí triúr ann (“There were three people there”).

Examples in Context

Irish	English	Note
Tá aon chat amháin sa teach.	There is one cat in the house.	aon … amháin marks exactly one.
Tá dhá chapall sa pháirc.	There are two horses in the field.	dhá lenites capall.
Cheannaigh mé trí leabhar.	I bought three books.	The noun remains singular in form.
Tá ceithre theach ar an tsráid.	There are four houses on the street.	ceithre causes lenition.
Tá cúig theach nua anseo.	There are five new houses here.	The number mutates teach to theach.
Chonaic sí sé chat.	She saw six cats.	sé causes lenition.
Tá seacht gcapall acu.	They have seven horses.	seacht eclipses capall.
D’oscail siad ocht mbosca.	They opened eight boxes.	b is eclipsed by m.
Tá naoi ndoras san fhoirgneamh.	There are nine doors in the building.	d is eclipsed by n.
Fuair mé deich bpunt.	I received ten pounds.	p is eclipsed by b.
Tá trí chat déag sa ghairdín.	There are thirteen cats in the garden.	The noun comes before déag.
Is é tríocha a cúig an uimhir.	The number is thirty-five.	Modern decimal counting form.
Tá beirt chairde liom.	Two friends are with me.	Personal numeral for two people.
Bhí triúr ann.	There were three people there.	The personal numeral stands alone.

Common Mistakes

Adding the counting particle before a noun

• Wrong: a trí leabhar
• Right: trí leabhar
• Why: Use a trí when saying “three” independently. Drop a when the number directly counts a noun.

Making the noun regularly plural as in English

• Wrong: dhá chapaill
• Right: dhá chapall
• Why: After a simple cardinal number, Irish normally uses the singular form of the noun. English plural logic does not transfer directly.

Forgetting the mutation

• Wrong: cúig teach; seacht capall
• Right: cúig theach; seacht gcapall
• Why: In the basic pattern, 2–6 trigger lenition and 7–10 trigger eclipsis.

Using aon without clarifying exact “one”

• Less clear: aon chat when you specifically mean “one cat and no more”
• Clear: aon chat amháin
• Why: amháin makes the exact numerical meaning explicit; aon on its own can also have an indefinite sense such as “any.”

Counting people like objects

• Awkward in the usual small-group sense: dhá duine
• Right: beirt or beirt daoine, depending on the construction and intended wording
• Why: Irish normally uses personal numerals for small groups of people. Learn beirt, triúr, and ceathrar early because they are frequent.

Putting déag before the noun

• Wrong: trí déag cat
• Right: trí chat déag
• Why: With 11–19, the counted noun is placed between the unit and déag.

Usage Notes

The form used for a number depends on what you are doing. Reciting a sequence favors a haon, a dó, a trí. Labels, bus routes, room numbers, sports scores, prices, and telephone numbers may be read according to local convention and the type of number. Listening to how native speakers read real numbers is therefore more useful than assuming every digit string follows one universal pattern.

Irish has significant dialect variation, and compound numbers are an area where traditional and decimal systems coexist. Forms such as fiche a haon are transparent to learners, while the traditional “unit and twenty” order remains alive in familiar contexts. Treat the variation as something to recognize, not as evidence that one speaker is necessarily wrong.

Currency and measurements may also affect noun forms. In everyday signage, international symbols and digits often reduce the amount of Irish grammar visibly present. In full sentences, however, the mutation and number pattern still matter.

Beyond the Basics

You do not need to master these details at A1, but they explain forms that will appear later.

First, the noun after a personal numeral is not simply the ordinary English-style plural. It is often a genitive plural form, and some common nouns have irregular forms: compare fear (“man”) with triúr fear, and bean (“woman”) with beirt bhan. This belongs to the wider Irish case system—a set of noun forms used for different grammatical relationships.

Second, a counted noun can influence words around it. Adjectives and articles have their own agreement and mutation rules, so a longer phrase is not always built by attaching an unchanged adjective to the short pattern learned here. Learn the number-plus-noun core first, then notice complete phrases in reading.

Third, older and traditional counting makes substantial use of twenties. You may encounter expressions organized around fiche rather than decimal tens, as well as established age expressions such as bliain is fiche. Modern Irish also uses decimal tens extensively. Recognising both systems is more important initially than producing every traditional compound without hesitation.

Finally, cardinal numbers answer “how many?” Ordinal numbers answer “which one in order?” Irish uses different words for these: aon is “one,” but an chéad is “the first”; dó/dhá is “two,” but an dara is “the second.” Do not build ordinals by merely changing the ending of the cardinal.

Practice Tips

1. Use three passes with the same noun. Say a haon, a dó, a trí; then aon chat, dhá chat, trí chat; then switch to capall and notice the mutations. This separates independent counting from noun counting.
2. Group numbers by mutation. Make one card for 2–6 labeled “lenition” and one for 7–10 labeled “eclipsis.” Practice with bád, cat, doras, fear, punt, and teach so that the spelling pattern becomes visual.
3. Learn people in chunks. Memorize beirt chairde, triúr páistí, and ceathrar múinteoirí as complete phrases. Later, when you study noun cases, you can analyze why the following form looks as it does.

Related Concepts

• Next step: Time and Dates — use numbers to tell the time and understand calendar expressions.
• Next step: Ordinal Numbers and Quantities — learn forms such as an chéad (“the first”), an dara (“the second”), and common quantity expressions.