The Article Theory in Welsh grammar is a fundamental aspect for understanding the use and function of articles in the Welsh language. In Welsh, articles play a crucial role in determining the definiteness and specificity of nouns.

According to this theory, there are six different types of articles in Welsh: y, yr, ‘r, un, yr un, and atgofion. The most commonly used articles are y, yr, and ‘r, which are used to specify definite nouns. Y is used before consonant-initial nouns, such as y ty (the house), while yr is used before vowel-initial nouns, such as yr anifail (the animal). The article ‘r is used before possessive pronouns, like ‘r tadau (the fathers).

Un and yr un are indefinite articles, which are used before singular nouns to indicate nonspecificity, e.g., un car (a car), yr un mwnci (a monkey). Lastly, atgofion functions as a verbal noun and translates to “memories,” indicating a plural and specific noun.

Understanding the Article Theory is essential for learners of Welsh to correctly use and comprehend articles in their speech and writing.