

Harry correctly notes that एतत् तत् चित्रम् (etat tat citram) and एषः सः ब्राह्मणः (eṣaḥ saḥ brāhmaṇaḥ) are morphologically identical in structure, differing only in gender (neuter vs. masculine). To understand why a textbook might mark the neuter version as "wrong" while accepting the masculine version, we must look through three specific lenses of Sanskrit Vyākaraṇa (grammar) and Nyāya (logic): classical idiom, syntactic ambiguity, and euphonic combination (Sandhi).
Here is the solution to the discrepancy:
1. The Classical Idiom of Recognition (प्रत्यभिज्ञा - pratyabhijñā)In an equational sentence where two pronouns are used to express "This is that [X]" or "That [X] is this", Sanskrit relies heavily on a specific logical sequence for the उद्देश्य (uddeśya - the subject) and the विधेय (vidheya - the predicate).
According to the classical idiom of recognition (प्रत्यभिज्ञा - pratyabhijñā) used heavily in Advaita Vedānta and Nyāya schools, the distant or past-referenced pronoun (तद् - tad / सः - saḥ) almost always precedes the proximate or present-referenced pronoun (एतद् - etad / एषः - eṣaḥ / इदम् - idam).
Analogy (उपमा): Imagine you are verifying someone's identity. You hold up an old photograph (the distant/known "That") and map it onto the live person standing in front of you (the proximate "This"). Sanskrit logic prefers establishing "That" first.
Examples:
Therefore, writing "एतत् तत् चित्रम्" (etat tat citram) feels backwards to a traditional scholar. The subject ("That known picture") should ideally come first, making "तत् एतत् चित्रम्" (tat etat citram) the idiomatic standard. When the textbook claims "the subject can't go first" here, it likely means that placing etat first reverses the natural subject-predicate relationship expected in this idiom.
2. Syntactic Ambiguity in the Neuter GenderWhy would Coulson penalize the neuter "एतत् तत्" (etat tat) but allow the masculine "एषः सः" (eṣaḥ saḥ)? The answer lies in case ambiguity.
In the neuter gender, the प्रथमा (prathamā - nominative case) and द्वितीया (dvitīyā - accusative case) forms are absolutely identical: एतत् (etat) and तत् (tat). Because Sanskrit word order is relatively free, placing two identical neuter pronouns next to each other without a verb (like asti - is) creates visual ambiguity. Out of context, "एतत् तत् चित्रम्" could be misparsed syntactically.
Conversely, in the masculine gender, the nominative forms एषः (eṣaḥ) and सः (saḥ) are distinctly different from their accusative forms (एतम् - etam, तम् - tam). Therefore, "एषः सः ब्राह्मणः" (eṣaḥ saḥ brāhmaṇaḥ) is uniquely and unmistakably nominative. Because there is zero risk of confusing the subject/predicate for a direct object, the author is more lenient with the word order here.
3. The Pāṇinian Sandhi PerspectiveFinally, there is a morphological elegance to the masculine sequence that makes it highly acceptable in continuous text.
According to Pāṇini, the nominative singular marker (सुँ - su, which becomes the visarga ḥ) of the pronouns etad and tad is dropped before any consonant (hal).
एतत्तदोः सुलोपोऽकोर्नञ्समासे हलि॥ [Pāṇini, Aṣṭādhyāyī, 6.1.132] Padaccheda (Word-split): एतद्-तदोः सु-लोपः अकः नञ्-समासे हलि। (etad-tadoḥ su-lopaḥ akaḥ nañ-samāse hali.)
Due to this rule, "एषः सः ब्राह्मणः" (eṣaḥ saḥ brāhmaṇaḥ) resolves beautifully and fluidly into एष स ब्राह्मणः (eṣa sa brāhmaṇaḥ). It lacks the clashing consonants found in the neuter एतत्तच्चित्रम् (etattaccitram). This phonetic fluidity often causes textbook authors to cite masculine double-pronouns as "correct" examples of Sandhi application, even if they slightly bend the strict subject-first pedagogical rules established in earlier chapters.
Summary: Harry Spier is structurally correct—the sentences are functionally identical. However, "एतत् तत् चित्रम्" is marked wrong because it breaks the classical idiom of recognition ("That" must precede "This") and risks accusative/nominative ambiguity. "एषः सः ब्राह्मणः" is allowed because its masculine markers definitively prove it is in the nominative case, making it syntactically unambiguous despite the word order.