vidhi rules

In the previous lessons, we defined a simple, concise, and expressive system for defining various groups of Sanskrit sounds. But our system is missing something obvious: a way to use the terms we've defined. It's as if we have a gourmet kitchen with the finest tools, the freshest ingredients, the most wonderful patrons — and no chef.

So in this lesson and the two that follow, we'll apply our system to a real problem: how to model and describe Sanskrit's sandhi changes. We'll do so by learning how to apply basic vidhi rules. And by learning how to do this, we will complete our small system and be ready to examine the rest of the Aṣṭādhyāyī.

vidhi literally means “rule” or “command.” Unlike saṃjñā rules that merely assign a label, or paribhāṣā rules that help us interpret rules correctly, vidhi rules are the core operations of the grammar. They add, remove, and modify different terms. And by applying them in the correct sequence, we create a correct Sanskrit expression.

How do we apply vidhi rules in the correct sequence? This simple question is surprisingly deep and profound, and we cannot give a proper answer to it for some time. A good rule of thumb is that we should apply the most specific rule we can.

But for now, let's focus on more concrete matters: what vidhi rules are, how we define them, and how we can use them to define sandhi rules.

Conditions for sandhi

As a reminder, sandhi is the name for Sanskrit's various sound changes. Sandhi occurs only in specific circumstances:

  • परः संनिकर्षः संहिता। १.४.१०९
    paraḥ saṃnikarṣaḥ saṃhitā (1.4.109)
    paraḥ saṃnikarṣaḥ saṃhitā
    Extremely close contact [of sounds] is called saṃhitā.

  • संहितायाम्। ६.१.७२
    saṃhitāyām (6.1.72)
    In saṃhitā, …

Rule 1.4.109 is a simple saṃjñā rule. But rule 6.1.72 is a new and different kind of rule. What does this rule do? Simply, it adds extra context for the rules that follow it. Such rules are called adhikāra (“government”) rules.

How many rules does an adhikāra apply to? Each adhikāra has a specific scope, which we can usually determine from context or from the rule itself. When in doubt, we can rely on expert commentaries to help us.

And as a quick note, perhaps you're wondering: how many different rule types are there? Different authors classify them in different ways, but in this series, we will use just five basic types: vidhi (operation), saṃjñā (definition), adhikāra (government), paribhāṣā (interpretation), and a fifth type called atideśa (analogy) that we will use later on.

Our first sandhi rule

Let's start the discussion with some small sandhi changes:

  • द्रौपदी अश्वम् इच्छति → द्रौपद्यश्वम् इच्छति
    draupadī aśvam icchati → draupadyaśvam icchati
    Draupadi wants a horse.

  • मधु अस्ति → मध्वस्ति
    madhu asti → madhvasti
    There is honey.

The basic idea is that if two non-similar vowels are in close contact (saṃhitā), then the first vowel should become a semivowel.

How might we capture this change? Pāṇini offers the following rule, but it is difficult to understand:

  • इको यणचि। ६.१.७७
    iko yaṇaci (6.1.77)
    ikaḥ yaṇ aci
    Of ik, there is yaṇ in ac [in saṃhitā].

Let's start with what we do know. We know that ik, yaṇ, and ac are all pratyāhāras:

  • ik refers to one of the vowels i, u, , and , and to any vowels similar to these four.

  • yaṇ refers to one of the four semivowels: y, v, r, and l.

  • ac refers to any vowel.

We also know that Sanskrit words express meanings through inflection. All three of these pratyāhāras are Sanskrit nouns, and they express different grammatical cases through different noun endings. (Roughly, a noun's case is the role it plays in the sentence.) So we have:

  • the sixth case (ik-aḥ), which can be translated as “of.”

  • the first case (yaṇ), which is usually the subject of a sentence.

  • the seventh case (ac-i), which can be translated as “in.”

Because we know what the rule should be, we can guess what the rule is trying to express. But this guesswork doesn't feel satisfying. It feels like something crucial is missing.

How to interpret cases in formal grammar

The solution is to rely on three new paribhāṣā rules. Together, they describe how we should interpret these cases in the context of formal grammar:

  • षष्ठी स्थानेयोगा। १.१.४९
    ṣaṣṭhī sthāneyogā (1.1.49)
    ṣaṣṭhī sthāne-yogā
    The sixth case can signify sthāne (in the place of).

  • तस्मिन्निति निर्दिष्टे पूर्वस्य। १.१.६६
    tasminniti nirdiṣṭe pūrvasya (1.1.66)
    tasmin iti nirdiṣṭe pūrvasya
    When the seventh case is specified, [substitution is] of the previous.

  • तस्मादित्युत्तरस्य। १.१.६७
    tasmādityuttarasya (1.1.67)
    tasmāt iti uttarasya
    When the fifth case [is specified, substitution is] of the next.

What do these rules mean? It's simple. In the context of a substitution:

  • the sixth case marks the term that will be replaced

  • the fifth case marks the term that must appear before the substitution

  • the seventh case marks the term that must appear after it

And by normal Sanskrit semantics, the first case will define the replacement. With these principles in mind, we can reinterpret the case semantics in rule 6.1.77:

  • ik is in the sixth case (ikaḥ), so it will be replaced.

  • yaṇ in the first case (yaṇ), so it is the substitute.

  • ac in the seventh case (aci), so it follows the substitution.

Now rule 6.1.77 has a clearer meaning:

  • इको यणचि। ६.१.७७
    iko yaṇaci (6.1.77)
    ikaḥ yaṇ aci
    An ik vowel is replaced with yaṇ when a vowel follows [in saṃhītā].

Substitution with two lists

There is still a subtle problem with rule 6.1.77 above: which yaṇ sound do we use? We know that y is the right choice, but the rule does not say so explicitly. So it would be legal to produce this incorrect result:

  • द्रौपदी अश्वम् इच्छति → * द्रौपद्रश्वम् इच्छति
    draupadī aśvam icchati → * draupadraśvam icchati
    Draupadi wants a horse.

Our rule is too loose. How do we fix this?

Pāṇini offers several rules for performing a substitution correctly, but just one is relevant to us here:

  • यथासंख्यमनुदेशः समानाम्। १.३.१०
    yathāsaṃkhyamanudeśaḥ samānām (1.3.10)
    yathā-saṃkhyam anudeśaḥ samānām
    Substitution of [items with] the same [size] is according to their relative number.

More plainly, rule 1.3.10 states that if a rule says to replace one list (call it A) with another (call it B) of the same size, what it really means is that we replace the item 1 of A with item 1 of B, item 2 of A with item 2 of B, and so on for the rest of the list.

Now rule 6.1.77 has a clear, consistent meaning:

  • इको यणचि। ६.१.७७
    iko yaṇaci (6.1.77)
    ikaḥ yaṇ aci
    An ik vowel is replaced by its respective yaṇ sound when a vowel follows [in saṃhitā].

If we return to our original example, we know that ik denotes the four vowels i, u, , and . And we know that yaṇ denotes the four semivowels y, v, r, and l. So by rule 1.3.10, we see what the correct replacements are:

  • इ → य्
    i → y

  • उ → व्
    u → v

  • ऋ → र्
    ṛ → r

  • ऌ → ल्
    ḷ → l

Therefore, the replacement for i is y, and we get our desired result:

  • द्रौपदी अश्वम् इच्छति → द्रौपद्यश्वम् इच्छति
    draupadī aśvam icchati → draupadyaśvam icchati
    Draupadi wants a horse.


Understanding rule 6.1.77 took a lot of work and several extra rules. But these new rules give us a precise and concise way to define different operations. We will use these rules over and over as we continue to explore the Aṣṭādhyāyī.

There's just one small catch: rule 6.1.77 has an important flaw. In the next lesson, we will fix this flaw and build a basic model for vowel sandhi.