BhG 2.12

syntax

jātu (never) aham (I) na āsam (I did not exist),
tvam na [āsīḥ] (you did not exist),
ime (these) janādhipāḥ (the rulers of men) na [āsan] (they did not exist) [iti]
tu na eva (but certainly not).
ataḥ param (hereafter) sarve (all) vayam (we) na bhaviṣyṣmaḥ (we will not exist) [iti]
na ca eva (and certainly not).

grammar

na	–	av. – not;
tu	–	av. – but, then, or, and;
eva	–	av. – certainly, just, merely;
aham	–	asmat sn. 1n.1 – I;
jātu	–	av. – at all, ever, once, some day;
na	–	av. – not;
āsam	–	√as (to be) Imperf. P 3v.1 – I was, I existed;
na	–	av. – not;
tvam	–	yuṣmat sn. 1n.1 –you;
na	–	av. – not;
ime	–	idam sn. 1n.3 m. – these;
janādhipāḥ	–	jana-adhipa 1n.3 m.; TP: janānām adhipā iti – the rulers of men (from: √jan – to be born, to produce, jana – man, people, creature; adhi – over, above, pa – ruler, in compounds shortened form of: pati, adhi-pa – ruler, king);
na	–	av. – not;
ca	–	av. – and;
eva	–	av. – certainly, just, merely;
na	–	av. – not;
bhaviṣyāmaḥ	–	√bhū (to be) Fut. P 3v.3 – we will be, we will exist;
sarve	–	sarva sn. 1n.3 m. – all;
vayam	–	asmat sn. 1n.3 – we;
ataḥ	–	av. – from this, hence, therefore (indeclinable ablative with an ending -tas);
param	–	av. – later, next, future (from: para – beyond, ancient, final, the best, the supreme);

textual variants

na tv evāhaṁ → na hy evāhaṁ / na evāhaṁ / na tv enāhaṁ (certainly indeed not me / certainly not me / but not this me);
neme → nāmī (named, bent);
caiva → caivaṁ (and thus);
vayam ataḥ → vayam itaḥ (we from here);

Śāṃkara

The key:
an excerpt from the commented verse
quotes from the scriptures
starting polemic

(Question): – Why do they deserve no grief? (Answer): – For, they are eternal. (Question): – How? (Answer): – The Lord says:		kutas te aśocyāḥ ? yato nityāḥ | kathaṃ ?
12. Never did I not exist, nor thou, nor these rulers of men;and no one of us will ever hereafter cease to exist.		na tv evāhaṃ jātu nāsaṃ na tvaṃ neme janādhipāḥ | na caiva na bhaviṣyāmaḥ sarve vayam ataḥ param ||2.12||
Never did I cease to exist; on the other hand, I always did exist; that is, through the past bodily births and deaths, I always existed.		na tv eva jātu kadācid ahaṃ nāsaṃ kintv āsam eva | atīteṣu dehotpatti-vināśeṣu ghaṭādiṣu viyad iva nitya eva aham āsam ity abhiprāyaḥ |
So also, never did you cease to exist; on the other hand, you always did exist. So, never did these rulers of men cease to exist; on the other hand, they always did exist.		tathā na tvaṃ nāsīḥ, kintv āsīr eva | tathā neme janādhipā āsan kintv āsann eva |
So, neither shall we ever cease to exist; on the other hand, we shall all certainly continue to exist even after the death of these bodies. As the Self, the Atman, we are eternal in all the three periods of time (past, present and future).		tathā na caiva na bhaviṣyāmaḥ, kintu bhaviṣyāma eva, sarve vayam ato ’smād deha-vināśāt param uttara-kāle ’pi | triṣv api kāleṣu nityā ātma-svarūpeṇa ity arthaḥ |
The plural ‚us’ is used with reference to the bodies that are different ; it does not mean that there are more than one Self.		deha-bhedānuvṛttyā bahu-vacanam, nātma-bhedābhiprāyeṇa ||2.12||

Rāmānuja

prathamaṃ tāvad ātmanāṃ svabhāvaṃ śṛṇu | ahaṃ sarveśvaras tāvad ato vartamānāt pūrvasmin anādau kāle na nāsam api tu āsam | tvan-mukhāś caite īśitavyāḥ kṣetrajñā na nāsan api tv āsan | ahaṃ ca yūyaṃ ca sarve vayam ataḥ param asmād anantare kāle na caiva na bhaviṣyāmaḥ, api tu bhaviṣyāma eva | yathā ahaṃ sarveśvaraḥ paramātmā nitya iti nātra saṃśayaḥ, tathaiva bhavantaḥ kṣetrajñā ātmāno’pi nityā eveti mantavyāḥ | evaṃ bhagavataḥ sarveśvarad ātmanāṃ parasparaṃ ca bhedaḥ pāramārthakaḥ, iti bhagavatā evoktam iti pratīyate |
ajñāna-mohitaṃ prati tan-nivṛttaye pāramārthika-nityatvopadeśa-samaye aham ‚tvam ‚ime’ sarve ‚vayam iti vyapadeśāt | aupādhikātma-bheda-vāde hy ātma-bhedasyātāttvikatvena tattvopadeśa-samaye bheda-nirdeśo na saṃgacchate | bhagavad-uktātma-bhedaḥ svābhāvika iti | śrutir apy āha—nityo nityānāṃ cetanaś cetanānām eko bahūnāṃ yo vidadhāti kāmān [śve.u. 6.13] iti | nityānāṃ bahūnāṃ cetanānāṃ ya ekaś cetano nityaḥ sa kāmān vidadhātīty arthaḥ |
ajñāna-kṛta-bheda-dṛṣṭi-vāde tu parama-puruṣasya paramārtha-dṛṣṭer nirviśeṣa-kūṭastha-nitya-caitanyātma-yāthātmya-sākṣāt-kārat nivṛttājñāna-tat-kāryatayā ajñāna-kṛta-bheda-darśanaṃ tan-mūlopadeśādi-vyavahāraś ca na saṃgacchante | [parama-puruṣo’py ajña iti pakṣe’rjuna-vākyāt parama-puruṣa-vākyasyājñāna-mūla-mithyārthatve viśeṣābhāvān na tasyopadeśa-rūpatvāt |]
atha parama-puruṣasyādhigatād dvaita-jñānasya bādhitānuvṛtti-rūpam idaṃ bheda-jñānaṃ dagdha-paṭādivan na bandhakam iti ucyate, naitad upapadyate | marīcikā-jala-jñānādikaṃ hi bādhitam anuvartamānam api na jalāharaṇādi-pravṛtti-hetuḥ | evam atrāpy advaita-jñānena bādhitaṃ bheda-jñānam anuvartamānam api mithyārtha-viṣayatva-niścayāt nopadeśādi-pravṛtti-hetuḥ bhavati | na ceśvarsya pūrvam ajñasya śāstrādhigata-tattva-jñānatayā bādhitānuvṛttiḥ śakyate vaktum | yaḥ sarvajñaḥ sarvavit [mu.u. 2.1.9] parasya śaktir vividhaiva śrūyate svābhāvikī jñāna-bala-kriyā ca [śve.u. 6.8]
vedāhaṃ samatītāni
vartamānāni cārjuna |
bhaviṣyāṇi ca bhūtāni
māṃ tu veda na kaścana [gītā 7.26] iti śruti-smṛti-virodhāt |
kiṃ ca, parama-puruṣaś cedānīntana-guru-paramparā cādvitīyātma-svarūpa-niścaye sati anuvartamāne’pi bheda-jñāne sva-niścayānurūpam advitīyam ātma-jñānaṃ kasmā upadiśatīti vaktavyam ? pratibimbavat pratīyamānebhyaḥ arjunādibhya iti cet, naitad upapadyate; na hy anunmattaḥ ko’pi maṇi-kṛpāṇa-darpaṇādiṣu pratīyamāneṣu svātma-pratibimbeṣu teṣāṃ svātmano’nanyatvaṃ jānan tebhyaḥ kam apy artham upadiśati |
bādhitānuvṛttir api tair na śakyate vaktum | bādhakenādvitīyātma-jñānena ātma-vyatirikta-bheda-jñana-kāraṇasyānāder vinaṣṭatvāt | dvi-candra-jñānādau tu candraikatva-jñānena pārmārthika-timirādi-doṣasya dvi-candra-jñāna-hetoḥ avinaṣṭatvād bādhitānuvṛttiḥ yuktā | anuvartamānam api prabala-pramāṇa-bādhitvenākiñcitkaram | iha tu bheda-jñānasya sa-viṣayasya sa-kāraṇasya apāramārthikatvena vastu-yāthātmya-jñāna-vinaṣṭatvāt na kathaṃcid api bādhitānuvṛttiḥ saṃbhavati | ataḥ sarveśvarasya idānīntana-guru-paramparāyāś ca tattva-jñānam asti ced bheda-darśana-tat-kāryopadeśādya-saṃbhavaḥ | bheda-darśnam astīti ced, ajñānasya tad-dhetoḥ sthitatvenājñatvād eva sutarām upadeśo na saṃbhavati |
kiṃ ca, guror advitīyātma-vijñānād eva brahma-jñānasya sakāryasya vinaṣṭatvāt śiṣyaṃ prati upadeśo niṣprayojanaḥ | gurus taj-jñānaṃ ca kalpitam iti cet, śiṣya-taj-jñānayor api kalpitatvāt tad apy anivartakam | kalpitatve’pi pūrva-virodhitvena nivartakam iti cet, tad ācārya-jñāne’pi samānam iti tad eka nivartakaṃ bhavatīty upadeśānarthakyam eva | iti kṛtam asamīcīna-vādair nirastaiḥ

Śrīdhara

aśocyatve hetum āha na tv evāham iti | yathāhaṃ parameśvaro jātu kadācit līlā-vigrahasyāvirbhāva-tirobhāvato nāsam iti tu naiva | api tv āsam eva anāditvāt | na ca tvaṃ nāsīḥ nābhūḥ, api tv āsīr eva | ime vā janādhipā nṛpā nāsann iti na, api tu āsann eva mad-aṃśatvāt | tathātaḥ param ita upary api na bhaviṣyāmo na sthāsyāma iti ca naiva, api tu sthāsyāma eveti janma-maraṇa-śūnyatvād aśocyā ity arthaḥ

Madhusūdana

commentary under the verse BhG 2.18

Viśvanātha

athavā sakhe tvām aham evaṃ pṛcchāmi | kiṃ ca prītyāspadasya maraṇe dṛṣṭe sati śoko jāyate, tatreha prītyāspadam ātmā deho vā ? sarveṣām eva bhūtānāṃ nṛpa svātmaiva vallabhaḥ [BhP 10.14.57] iti śukokter ātmaiva prīty-āspadam iti cet tarhi jīveśvara-bhedena dvividhasyaivātmano nityatvād eva maraṇābhāvād ātmā śokasya viṣayo nety āha na tv evāham iti | ahaṃ paramātmā jātu kadācid api pūrvaṃ nāsam iti na, api tv āsam eva | tathā tvam api jīvātmā āsīr eva | tatheme janādhipā rājānaś ca jīvātmāna āsann eveti prāg-abhāvābhāvo darśitaḥ | tathā sarve vayam ahaṃ tvam ime janādhipāś cātaḥ paraṃ na bhaviṣyāmo na sthāsyāma iti na, api tu sthāsyāma eveti dhvaṃsābhāvaś ca darśita iti paramātmano jīvātmanāṃ ca nityatvād ātmā na śoka-viṣaya iti sādhitam | atra śrutayaḥ – nityo nityānāṃ cetanaś cetanānām eko bahūnāṃ yo vidadhāti kāmān [ŚvetU 6.13] ity ādyāḥ

Baladeva

evam asthāna-śocitvād apāṇḍityam arjunasyāpādya tattva-jijñāsuṃ niyojitāñjaliṃ taṃ prati sarveśvaro bhagavān nityo nityānāṃ cetanaś cetanānām eko bahūnāṃ yo vidadhāti kāmān [ŚvetU 6.13] iti śruti-siddhaṃ svasmāj jīvānāṃ ca pāramarthikaṃ bhedam āha na tv evāham iti | he arjuna ! ahaṃ sarveśvaro bhagavān itaḥ
pūrvasminn ādau kāle jātu kadācin nāsam iti na, api tv āsam eva | tathā tvam arjuno nāsīr iti na, kintv āsīr eva | ime janādhipā rājāno nāsann iti na, kintv āsann eva | tathetaḥ parasminn ante kāle sarve vayam ahaṃ ca tvaṃ ca ime ca na bhaviṣyāma iti na, kintu bhaviṣyāma eveti | sarveśvaravaj jīvānāṃ ca traikālika-sattā-yogitvāt tad-viṣayako na śoko yukta ity arthaḥ | na cāvidyā-kṛtatvād vyavahāriko ‚yaṃ bhedaḥ | sarvajñe bhagavaty avidyā-yogāt | idaṃ jñānam upāśritya ity ādinā mokṣe ‚pi tasyābhidāsyamānatvāc ca | na cābhedajñasyāpi harer bādhitānuvṛtti-nyāyeneyam arjunādi-bheda-dṛṣṭir iti vācyam | tathā saty upadeśāsiddheḥ | maru-marīcikādāv udaka-buddhir bādhitāpy anuvartamānā mithyārtha-viṣayatva-niścayān nodakāharaṇādau pravartayed evam abheda-bodha-bādhitāpy anuvartamānārjunādi-bheda-dṛṣṭis tattva-niścayān nopadeśādau pravartayiṣyatīti yat kiñcid etat |
nanu phalavaty ajñāte ‚rthe śāstra-tātparya-vīkṣaṇāt tādṛśo ‚bhedas tātparya-viṣayo vaiphalyāj jñātatvāc ca | bhedas tad-viṣayo na syāt, kintu adbhyo vā eṣa prātar udety apaḥ sāyaṃ praviśati ity ādi-śruty-arthavad anuvādya eva sa iti cen mandam etat | pṛthag ātmānaṃ preritāraṃ ca matvā juṣṭas tatas tenāmṛtatvam eti [ŚvetU 1.6] ity ādinā bheda evāmṛtatva-phala-śravaṇāt | viruddha-dharmāvacchinna-pratiyogikatayā loke tasyājñātatvāc ca | te ca dharmā vibhutvāṇutva-svāmitva-bhṛtyatvādayaḥ śāstraika-gamyā mitho viruddhā bodhyāḥ | abhedas tv aphalas tatra phalānaṅgīkārāt | ajñātaś ca śaśa-śṛṅgavad asattvāt | tasmāt paramārthikas tad-bhedaḥ siddhaḥ