Mahabhasya.

The Mahabhasya on Astadhyayi 1.3.1 contains a skillfully arranged discussion of topics related to units which should be called dhatu. the bhasya begins with a discussion of why the sutra has bhuvadya with uv and cities the first half of the sloka vartika stating that "v" is used for the sake of auspiciousness.

Step-by-step derivation of भवति (bhavati) – “he/she/it becomes”:

1. Start with the dhātu:

भू – this is the root meaning to be or to become.

2. Apply a tense suffix (pratyaya):

We choose the laṭ lakāra, which represents the present tense.

According to Pāṇini’s rules, the suffix ti is added for the third person singular in present tense.

So:

भू + laṭ (3rd person singular) → bhū + ti

But we need an intermediate step: before the personal ending "ti" is added, a special tense marker suffix laṭ-ādeśa, like laṭ-pratyaya, adds a vowel or modifies the root.

3. Apply guṇa (vowel strengthening):

According to grammatical rules, before the suffix is added, the vowel ū in bhū undergoes guṇa (a kind of vowel gradation), becoming o.

But in certain conjugations like present tense, bhū is actually converted to bhav. This is a special case where "ū" becomes "ava" due to internal grammatical transformation.

So:

भू → भव

4. Add the suffix:

Now we add the present tense third person singular ending -ti.

So:

भव + ति → भवति

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Final Word:

भवति = He/She/It becomes or is (in the sense of becoming)

This entire derivation is enabled by Aṣṭādhyāyī 1.3.1, which identifies bhū and similar roots as dhātus, allowing grammatical operations (like adding pratyayas) to take place.