Bhashya
वाच ऋगस इत्युक्तम् , कतमा सा ऋक् ? कतमत्त-त्साम ? कतमो वा स उद्गीथ ? कतमा ऋतमेति वीप्सा आदरा-र्था ।ननु 'वा बहूना जातिपरिप्रश्ने डतमच्' इति डतमच्प्र-त्यय इष्ट , न हि अत्र ऋग्जातिबहुत्वम् , कथ डतमच्प्रयोग ?नैष दोष , जातौ परिप्रश्नो जातिपरिप्रश्न — इत्येतस्मिन्विग्रहेजातावृग्यक्तीना बहुत्वोपपत्ते , न तु जाते परिप्रश्न इतिविगृह्यते ।ननु जात परिप्रश्न —इत्यस्मिन्विग्रहे 'कतम कठ 'इत्याद्युदाहरणमुपपन्नम् , जातौ परिप्रश्न इत्यत्र तु न युज्यते—तत्रापि कठादिजातावेव व्यक्तिबहुत्वाभिप्रायेण परिप्रश्न इत्य-दोष ।यदि जाते परिप्रश्न स्यात् , 'कतमा कतमर्कु' इत्याद्वावुपसंख्यान कर्तव्यं स्यात् ।विमृष्टं भवति विमर्श कृतो भवति ॥
In plain words
It has been stated that the Rig is the essence of speech. But which indeed is that Rig? Which is that Saman? Which is that Udgitha? The repetition of the question is meant to show earnest eagerness. One might object: 'Is not the suffix datamac used only when choosing from among many of a certain class? Since there are not multiple classes of Rig here, how can this suffix be grammatically justified?' This is not a valid objection. If we analyze the compound as 'an inquiry among the individuals of a class,' the multiplicity of individual Rig verses within that single class makes perfect sense; we do not analyze it as 'an inquiry about classes themselves.' If it were an inquiry about classes, we would have to invent a special grammatical exception for phrases like 'which Rig?' Therefore, 'it is deliberated' simply means that a deep, thorough investigation has been conducted.
Close to the Sanskrit
It was said that the Rig is the essence of speech. Which is that Rig? Which is that Saman? Which indeed is that Udgitha? The repetition 'which Rig' is for the sake of showing eagerness. An objection: Is it not that the suffix 'datamac' is prescribed by the rule 'or among many in an inquiry of genus'? Indeed, there is no multiplicity of the genus of Rig here; how then is the suffix 'datamac' used? This is not a fault. In the compound analysis 'inquiry in a genus is jati-pariprasna', the multiplicity of individual Rig verses within the genus is logical; but it is not analyzed as 'inquiry of a genus'. Objection: In the analysis 'inquiry of a genus', the example 'which Katha?' is logical, but 'inquiry in a genus' is not logical here. Answer: There too, the inquiry is with the intention of multiplicity of individuals within the Katha genus itself, so there is no fault. If it were 'inquiry of a genus', then an additional rule like 'katama, katamad rk' would have to be made. 'Vimrstam bhavati' means 'deliberation is made'.