In English we speak of - man; a man; the man. In Gaelic these would be - duine; duine an duine, respectively. In other words, only the definite article "the" is translated in Gaelic and the base form of it is "an".
This definite article "an", however, changes in form according to the number, gender, case, and initial letter of the noun which it qualifies. The different forms in the nominative singular are as follows -
We shall now take those forms in succession and try to illustrate their uses and changes.
But one further remark.
In English we speak of the man, and the men; in Gaelic these would be rendered as an duine, and na daoine, respectively: i.e. in Gaelic we have a different form of the article in the nominative plural, namely na.