स्वं रूपं शब्दस्याशब्दसंज्ञा

This is a rule of interpretation. The word स्वं which means 'one's own' denotes 'the meaning,' and the word रूप denotes 'the individual form of a word.' The sense of the sutra is that a word denotes both things expressed by those two words स्वं and रूप, viz., its meaning, and its form. Thus a rule applicable to अग्नि will be applicable to the word composed of अ, ग्, न्, इ and not to the words synonymous with agni, such as, पाककः, ज्वलनः &c.

In this science, therefore, the very word-form is to be taken, and understood and operated upon, and not external sense: with the exception of words which are definitions, in the latter case the things defined are to be taken.

This sutra is begun in order to remove the difficulty which might otherwise arise from a consideration that a word connotes a certain meaning, and as no grammatical operation is possible in a concrete object, we must take the words having the same meaning. As when a person is called to bring a 'cow,' he brings the animal cow, and not the letters c, o, w. It may therefore be said, that as no grammatical operation is possible in a material thing, we may take all the names synonymous with the word and operate upon them; this sutra removes that doubt.

Thus the sutra अग्नेर्ढक् 4.2.33 declares:- \that the affix 'dhak' comes after the word 'agni'.\ Thus अग्नि + ढक् = आग्नेयम् \belonging to agni,\ as in the following sentence आग्नेयमष्टाकपालं निर्वपेत्. Here the word अग्नि indicates the individual word-form अग्नि and not its synonyms. Similarly sutra 4.2.19 declares :- 'let there be optionally ठक् after उदश्वित्.' As औदश्वित्कम् 7.3.50 and 7.3.51 or औदश्वितम्. The rule applies to the word-form 'udasvita' meaning 'curd-milk' and not to तक्र, अरिष्ट, कालशेप, दण्डाहत and मथित, which are synonyms.

There is an important exception to this rule, and that is in favour of terms which are technical terms of Grammar and have been so defined.

Thus दाधाघ्वदाप् (1. 1. 20) and तरप्तमपौ घः 1.1.22. Here the words 'घु' and 'घ' denote the words connoted by those terms and not to their word-form. There are, however, some sutras in Panini which are apparently exceptions to this rule. These exceptions have been arranged under four heads, technically called सित्, पित्, जित्, and झित्. When there is a rule about a word, it may mean that very word-form, or words representing species falling under that word, or words which are synonymous with it. Thus rule 2.4.12 declares, :- \वृक्ष 'tree' मृग 'deer,' तृण 'grass,' &c., may optionally be compounded as dvandva.\ Here the word वृक्ष stands as a generic name for the species falling under it, and does not represent the word-form, वृक्ष. Thus we have dvandva-compound of प्लक्ष + न्यग्रोध, as प्लक्षन्यग्रोधम् or प्लक्षन्यग्रोधाः । Such sutras are called सित्.

Then in sutra 3.4.40, we have an example of पित्. That sutra means \the word पुष 'to feed' takes the affix णमुल (अम्) when compounded with the word स्व.\ Here the word 'स्व' means both the word-form स्व, as well as the synonyms of स्व and the species of स्व. Thus स्व and धन 'wealth' are synonyms; while स्व 'wealth' and गो 'cow' are genus and species. Thus स्व + पुष् + णमुल् = स्वपोषम्. Similarly रैपोषम्, धनपोषम्, गोपोषम्, अश्वपोषम्. Such sutras are called पित्.

Then in sutra 2.4.23, we have an example of जित्. \A Tatpurusha compound ending with the word सभा 'court' is neuter, provided that it is preceded by the word raja, or by a word denoting a non-human being.\ Here the synonyms only of the word 'raja' are taken, and neither the word-form 'raja,' nor the special instances falling under it. Thus इन 'king' + सभा = इनसभम् 'king's assembly,' ईश्वर + सभा = ईश्वरसभम् 'king's assembly.' But not राजसभम्, but राजसभा. Nor can we take particular kings, such as चन्द्रगुप्त or पुष्पमित्र. In their case we must have पुष्पमित्रसभा, चन्द्रगुप्तसभा.

Then in sutra 4.4.35, we have an example of झित्. The sutra means \the words पक्षि 'bird' मत्स्य 'fish' मृग 'deer,' take the affix ठक् when the meaning is the killer thereof.\ Here the words पक्षि &c. denote both the word-forms पक्षि &c. as well as the species denoted by those terms, but not their synonyms. Thus पक्षि + ठक् = पाक्षिकः 'a bird-killer,' मात्स्यिकः, 'a fish-catcher.' शकुनि + ठक् = शाकुनिकः 'a vulture-killer.' But we cannot take the synonyms of 'पक्षि,' &c. except in the case of 'मत्स्य,' when we may take the word 'मीन.' As मात्स्यिकः and मैनिकः a fish killer.',