The Tense Comparison Theory in Welsh Grammar is an important aspect that students must understand in order to properly construct sentences in various tenses. This theory explains the differences in verb endings and provides guidance on which tense should be used in different situations.

In Welsh, there are three primary tenses: past, present, and future. Each tense has a variety of different verb endings based on factors such as person, number, and affirmative/negative.

The past tense is used to describe actions that have already happened. It is formed by adding the appropriate verb endings to the stem of the verb.

The present tense is used to describe actions that are happening currently or actions that happen regularly. The verb endings in the present tense are generally the same as the verb endings in the past tense, but there are a few exceptions.

The future tense is used to describe actions that will happen in the future. It is formed by adding the appropriate verb endings to the stem of the verb, and it also includes a separate form for negative statements.

Overall, understanding the Tense Comparison Theory in Welsh Grammar is crucial for students to accurately communicate in different tenses in the Welsh language.