Ceacht 12
ar	on	prep.	
an bord	the table	[art]+[n m1]	
ar an mbord	on the table	[prep.]+ [art.]+[n m1  # ecl.#]	
an t-arán	the bread	[art]+[n m1  # prefix#]	
an t-im	the butter	[art]+[n m2  # prefix#]	
an t-uisce	the water	[art]+[n m4  # prefix#]	
an bainne	the milk	[art]+[n m4]	
an tae	the tea	[art]+[n m4]	
an siúcra	the sugar	[art]+[n m4]	
gach	every	determiner	
gach rud	everything	[a + n.],	
cinnte	sure	a.	
crúiscín	jug	n m4	
pláta	plate	n m4	
sa chrúiscín	in the jug	prep phrase # len.#	
ar an bpláta	on the plate	[prep.]+[art]+[n m4 # ecl.#]	
níl a fhios agam	I don’t know	sentence # len.#	
a mhamaí	(addressing) mammy	voc case # len.#	

When "ar" is used with the singular definite article "an" it causes eclipsis
to the consonants B, C, F, G or P.  e.g. ar an mbord - on the table

The little word sa (in the) causes Lenition..

Here is a summary of the changes which occur due to Lenition, Eclipsis & prefixes

	Modification	
Initial
letter	lenition	eclipsis	prefix t-2	prefix h	
		
a			t-a	ha	
b	bh	mb			
c	ch	gc			
d	dh	nd			
e			t-e	he	
f	fh	bhf			
g	gh	ng			
i			t-i	hi	
m	mh				
o	__		t-o	ho	
P	ph	bp			
s	Sh1		ts		
t	th	dt			
u			t-u	hu	
Based on table produced by Larry Ackerman

1 Except when the 2nd letter in the initial word is C, F, M, P, T, V.
2 a hyphen is not inserted before an uppercase letter.