Substitution 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 own a gourmet restaurant with the finest tools, the freshest ingredients, the most wonderful customers — 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. Along the way, we'll complete our system by learning how to define substitution rules within Pāṇini's framework. And once we have done so, we will be ready to explore the rest of the grammar.

Conditions for sandhi

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

Rule 1.4.109 is similar to rules we have seen already. 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. The scope of an adhikāra is usually clear from context.

Our first substitution rule

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

The idea is that if two non-similar simple vowels are in close contact, and if the first vowel is not a, 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:

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, ṛ, and ḷ, as well as the vowel similar to those four.

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

• 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:

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

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

• ac in the seventh case (aci), 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 rules. All of them are instructions for how we should interpret these cases in the context of formal grammar:

With these rules in mind, we can reinterpret the case semantics in rule 6.1.77:

• ik 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:

But there is still a subtle problems with this rule: which yaṇ sound do we use? We know that ya is the right choice, but the rule does not tell us which is correct. So perhaps we could even do this:

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

Substitution with two lists

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

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

Now rule 6.1.77 has a clear, consistent meaning:

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

Therefore, the replacement for i is y:

Review

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 substitution rules. We will use these rules over and over as we continue to explore the system.

There's just one small catch: rule 6.1.77 has an important flaw. In the next lesson, we will fix this flaw and further examine how Pāṇini models the Sanskrit sandhi system.