BhG 18.1

syntax

arjuna (Arjuna) uvāca (he spoke):
he keśi-niṣūdana (O Keśiniṣūdana!) he mahā-bāho (O mighty-armed one!) he hṛṣīkeśa (O Hṛṣīkeśa!),
sannyāsasya (of renunciation) tyāgasya ca (and abandonment) tattvam (the truth) pṛthak (separately) veditum (to know) icchāmi (I desire).

grammar

arjunaḥ	–	arjuna 1n.1 m. – white, clear, Arjuna;
uvāca	–	√vac (to speak) Perf. P 1v.1 – he spoke;
saṁnyāsasya	–	saṁnyāsa 6n.1 m. – of laying aside, of resignation, of renunciation (from: sam-ni-√as – to lay aside, to renounce, to give up);
mahābāho	–	mahā-bāhu 8n.1 m.; BV: yasya bāhū mahāntau staḥ saḥ – O mighty-armed one! (from: √mah – to magnify, mahant – great; √baṁh – to grow, to increase, bāhu – the arm);
tattvam	–	tat-tva abst. 2n.1 n. – truth, reality (from: tat – that);
icchāmi	–	√iṣ (to desire) Praes. P 3v.1 – I desire;
veditum	–	√vid (to know, to understand) inf. – to know, to learn;
tyāgasya	–	tyāga 6n.1 m. – of leaving, of abandoning (from: √tyaj – to abandon, to give up);
ca	–	av. – and;
hṛṣīkeśa	–	hṛṣīkeśa 1n.1 m. – erect hair, Hṛṣīkeśa (from: √hṛṣ – to be excited; hṛṣī – erect; keśa – hair); or TP: hṛṣīkāṇām / indriyāṇām īśa iti – lord of the senses (from: hṛṣīka – an organ of senses; √xīś – to own, to reign, īśa – ruler, lord);
pṛthak	–	av. – separately, one by one (from: √pṛth – to extend);
keśi-niṣūdana	–	keśi-niṣūdana 8n.1 m.;TP: keśinaḥ niṣūdaneti – O killer of Keśin! (from: keśa – hair; -in, -min, -vin – sufixes meaning one who possesses; ni-√sūd – to kill, niṣūdana – killing, destroying)

textual variants

saṁnyāsasya → saṁnyāsas tu (but renunciations);
pṛthak keśi-niṣūdana → pṛthak keśi-nisūdana / pṛthak karma-niṣūdana (separately, O killer of Keśin! / separately, O killer of activity!);

The first pada of verse 18.1 is the same as the first pada of verse BhG 5.6;

Śāṃkara

sarvasyaiva gītāśāstrasyārtho’smin adhyāye upasaṃhṛtya sarvaś ca vedārtho vaktavyaḥ ity evam artho’yam adhyāya ārabhyate | sarveṣu hy atīteṣu adhyāyeṣūkto’rtho’sminn adhyāye’vagamyate | arjunas tu saṃnyāsa-tyāga-śabdārthayor eva viśeṣa-bubhutsur uvāca—

pūrvādhyāye śraddhā-traividhyenāhāra-yajña-tapo-dāna-traividhyena ca karmiṇāṃ traividhyam uktaṃ sāttvikānām ādānāya rājasa-tāmasāṃ ca hānāya | idānīṃ tu saṃnyāsa-traividhya-kathanena saṃnyāsinām api traividhyaṃ vaktavyam | tatra ttva-bodhānantaraṃ yaḥ phala-bhūtaḥ sarva-karma-saṃnyāsaḥ sa caturdaśe’dhyāye guṇātītatvena vyākhyātatvān na sāttvika-rājasa-tāmasa-bhedam arhati | yo’pi tattva-bodhāt prāk tad-arthaṃ sarva-karma-saṃnyāsas tattva-bubhutsayā vedānta-vākya-vicārāya bhavati so’pi traiguṇya-viṣayā vedā nistraiguṇyo bhavārjuna ity ādinā nirguṇatvena vyākhyātaḥ | yas tv anutpanna-tattva-bodhānām anutpanna-tattva-bubhutsānāṃ ca karma-saṃnyāsaḥ sa saṃnyāsī ca yogī ca ity ādinā gauṇo vyākhyātas tasya traividhya-sambhavāt tad-viśeṣaṃ bubhutsuḥ arjuna uvāca saṃnyāsasyeti |

aviduṣām anupajāta-vividiṣāṇāṃ ca karmādhikṛtānām eva kiṃcit karma-parigrahena kiṃcit karma-parityāgo yaḥ sa tyāgāṃśa-guṇa-yogāt saṃnyāsa-śabdenocyate | etādṛśasyāntaḥ-karaṇa-śuddhy-artham avidvat-karmādhikāri-kartṛkasya saṃnyāsasya kenacid rūpeṇa karma- tyāgasya tattvaṃ svarūpaṃ pṛthak sāttvika-rājasa-tāmasa-bhedena veditum icchāmi | tyāgasya ca tattvaṃ veditum icchāmi |

kiṃ saṃnyāsa-tyāga-śabdau ghaṭa-paṭa-śabdāv iva bhinna-jātīya-padārthau kiṃ vā brāhmaṇa-parivrājaka-śabdāv ivaika-jātīyārthau | yady ādyas tarhi tyāgasya tattvaṃ saṃnyāsāt pṛthag veditum icchāmi | yadi dvitīyas tarhy avāntaropādhi-bheda-mātraṃ vaktavyam | eka-vyākhyānenaivobhayaṃ vyākhyātaṃ bhaviṣyati |
mahābāho keśiniṣūdaneti sambodhanābhyāṃ bāhyopadrava-nivāraṇa-svarūpa-yogyatā-phalopadhāne pradarśite | hṛṣīkeśa ity antar-upadrava-nivāraṇa-sāmarthyam iti bhedaḥ | atyanurāgāt sambodhana-trayam |
atrārjunasya dvau praśnau | karmādhikāri-kartṛkena pūrvokta-yajñādi-sādharmyeṇa saṃnyāsa-śabda-pratipādyatvena ca guṇātīta-saṃnyāsa-dvaya-sādharmyeṇa traiguṇya-sambhavāsambhavābhyāṃ saṃśayaḥ prathamasya praśnasya bījam | dvitīyasya tu saṃnyāsa-tyāga-śabdayoḥ paryāyatvāt karma-phala-tyāga-rūpeṇa ca vailakṣaṇyokteḥ saṃśayo bījaṃ saṃnyāsatyāgaśabdau

Rāmānuja

atītenādhyāyadvayena abhyudayaniśśreyasasādhanabhūtaṃ vaidikam eva yajñatapodānādikaṃ karma, nānyat; vaidikasya ca karmaṇas sāmānyalakṣaṇaṃ praṇavānvayaḥ; tatra mokṣābhyudayasādhanayor bhedaḥ tatsacchabdanirdeśyatvena; mokṣasādhanaṃ ca karma phalābhisandhirahitaṃ yajñādikam; tadārambhaś ca sattvodrekād bhavati; sattvavṛddhiś ca sāttvikāhārasevayā ityuktam / anantaraṃ mokṣasādhanatayā nirdiṣṭayos tyāgasaṃnyāsayor aikyam, tyāgasya ca svarūpam, bhagavati sarveśvare ca sarvakarmaṇāṃ kartṛtvānusandhānam, sattvarajastamasāṃ kāryavarṇanena sattvaguṇasyāvaśyopādeyatvam, svavarṇocitānāṃ karmaṇāṃ paramapuruṣārādhanabhūtānāṃ paramapuruṣaprāptinirvartanaprakāraḥ, kṛtsnasya gītāśāstrasya sārārtho bhaktiyoga ity ete pratipādyante / tatra tāvat tyāgasaṃnyāsayor pṛthaktvaikatvanirṇayāya svarūpanirṇayāya cārjunaḥ pṛcchati

tyāgasaṃnyāsau hi mokṣasādhanatayā vihitau, „na karmaṇā na prajayā dhanena tyāgenaike amṛtatvam ānaśuḥ vedāntavijñānasuniścitārthās saṃnyāsayogād yatayaś śuddhasattvāḥ / te brahmaloke tu parāntakāle parāmṛtāt parimucyanti sarve//” ityādiṣu / asya saṃnyāsasya tyāgasya ca tattvam yāthātmyaṃ pṛthak veditum icchāmi / ayam abhiprāyaḥ kim etau saṃnyāsatyāgaśabdau pṛthagarthau, utaikārthav eva yadā pṛthagarthau, tadā anayoḥ pṛthaktvena svarūpaṃ veditum icchāmi; ekatve ‚pi tasya svarūpaṃ vaktavyam iti

Śrīdhara

atra ca –
sarva-karmāṇi manasā
sannyasyāste sukhaṃ vaśī | (Gītā 5.13)
sannyāsa-yoga-yuktātmā (Gītā 9.28)
ity ādiṣu karma-sannyāsa upadiṣṭaḥ | tathā –
tyaktvā karma-phalāsaṅgaṃ
nitya-tṛpto nirāśrayaḥ |
sarva-karma-phala-tyāgaṃ
tataḥ kuru yatātmavān || (Gītā 4.20)
ity ādiṣu ca phala-mātra-tyāgena karmānuṣṭhānam upadiṣṭam | na ca paraspara-viruddhaṃ sarvajñaḥ parama-kāruṇiko bhagavān upadiśet | ataḥ karma-sannyāsasya tad-anuṣṭhānasya cāvirodha-prakāraṃ bubhutsur arjuna uvāca sannyāsasyeti | bho hṛṣīkeśa sarvendriya-niyāmaka | he keśī-nisūdana keśī-nāmno mahato hayākṛteḥ daityasya yuddhe mukhaṃ vyādāya bhakṣayitum āgacchato atyantaṃ vyātte mukhe vāma-bāhuṃ praveśya tat-kṣaṇam eva vivṛddhena tenaiva bāhunā karkaṭikā-phalavat taṃ vidārya nisūditavān | ataeva he mahābāho iti sambodhanam | sannyāsasya tyāgasya ca tattvaṃ pṛthag vivekena veditum icchāmi

Viśvanātha

anantarādhyāye –
tad ity anabhisandhāya
phalaṃ yajña-tapaḥ-kriyāḥ |
dāna-kriyāś ca vividhāḥ
kriyante mokṣa-kāṅkṣibhiḥ || (Gītā 17.25)

ity atra bhagavad-vākye mokṣa-kāṅkṣi-śabdena sannyāsina eva ucyante | anye vā yady anya eva te, tarhi – sarva-karma-phala-tyāgaṃ tataḥ kuru yatātmavān iti (Gītā 12.11) tvad-uktānāṃ sarva-karma-phala-tyāgināṃ teṣāṃ sa tyāgaḥ kaḥ | sannyāsināṃ ca ko sa sannyāsa iti vivekato jijñāsur āha sannyāsasyeti | pṛthag iti yadi sannyāsa-tyāga-śabdau bhinnārthau tadā sannyāsasya tyāgasya ca tattvaṃ pṛthag veditum icchāmi | yadi tv ekārthau tāv api tvan-mate anya-mate vā tayor aikyārtham arthād ekārthatvam iti pṛthag veditum icchāmi | he hṛṣīkeśeti mad-buddheḥ pravartakatvāt tvam eva imaṃ sandeha-mukhāpayasi | keśi-nisūdana iti taṃ ca sandehaṃ tvam eva keśinam iva vidārayasīti bhāvaḥ | mahābāho iti tvaṃ mahā-bāhu-balānvito ‚haṃ kiñcid bāhubalānvita ity etad aṃśenaiva mayā saha sakhyaṃ tava | na tu sārvajñyādibhir aṃśair atas tvad-datta-kiñcit-sakhya-bhāvād eva praśne mama niḥśaṅkateti bhāvaḥ

Baladeva

sarva-karmāṇi manasā sannyasyāste sukhaṃ vaśī | (Gītā 5.13) ity ādau sannyāsa-śabdena kim uktam — tyaktvā karma-phalāsaṅgaṃ (Gītā 4.20) ityādau tyāga-śabdena ca kim uktaṃ bhagavatā tatra sandihāno ‚rjunaḥ pṛcchati sannyāsasyeti | sannyāsa-tyāga-śabdau śaila-taru-śabdāv iva vijātīyārthau kiṃ vā kuru-pāṇḍava-śabdāv iva sajātīyārthau | yady ādyas tarhi sannyāsasya tyāgasya ca tattvaṃ pṛthag-veditum icchāmi | yadyantas tarhi tatrāvāntaropādhi-mātraṃ bhedakaṃ bhāvi, tac ca veditum icchāmi | he mahābāho kṛṣṇa hṛṣīkeśeti dhī-vṛtti-prerakatvāt tvam eva mat-sandeham utpādayasi | keśi-nisūdaneti tvaṃ mat-sandehaṃ keśinam iva vināśayeti