Something that does not erode, or something from which nothing exude— na kṣarati. Imperishable. Especially in Sāṃkhya (Sankhya) philosophy, akṣara (akshara) is known as the ‘sākṣī cetā nirguṇa‘ theory of Man [that considers man as conscious and neutral observer]. Bhagavadgītā (Bhagavadgita), while determining the difference between a corporeal being and god, has said that there are two kinds of men in this world— those who decay (kṣara; kshara) and those who do not (akṣara)—

dvāvimau puruṣau loke kṣaraścākṣara eva ca;

kṣaraḥ sarbāṇi bhūtāni kūṭastho’kṣara ucyate.

Here, Śrīdharasvāmī (Sridharaswami) the annotator, has written that kṣara denotes all perishable entities in the world. Everything, from Brahmā (Brahma) to all immovable objects, are perishable. And ‘Akṣara‘ is one who is indestructible, immortal, and kūtastha (kutastha) or eternal. Kūṭa means heap. A mountain, which is a great heap of stones, does not suffer any damage if a portion of it breaks away, and remains unaffected. Similarly, akṣara is an unmoved, yet conscious Man. Mahābhārata (Mahabharata) says, “That which has been called perishable and into which the world has diffused after being created—I wish to hear about those destructible things. And I also wish to hear about that which is imperishable, the absolute, benignant and transcendental brahma”—

yaccākṣaramiti proktaṃ śivaṃ anāmayam.

• The last among the twenty four theories in Sāṁkhya philosophy is that of the Supreme Being or puruṣa (purusha), who is neither Nature nor Transformation of the energy. This Supreme Being is the omnipresent spirit of the world, who has been referred to as the One and only, and imperishable (akṣara)—

sāṃkhye ca paṭhyate śāstrenāmabhirbahudhātmakaḥ;

vicitrarūpo viśvātmā ekākṣara iti smṛtaḥ.

Puruṣa, in Sāṃkhya philosophy, has been identified as an absolute theory, an unalterable, imperishable puruṣa. Thus, Hiraṇyagarbha (Hiranyagarbha), Hari, Śiva (Shiva), Viṣṇu (Vishnu), and God have all been classified as ‘akṣara‘—

yadakṣaram athāvyakta īśaṃ lokasya bhāvanam.

• The word ‘akṣara‘ has been mainly used as a synonymous word to denote the supreme philosophy of brahma in ancient times. In the first quarter of Vedāntasūtras, there are at least three sutras  that discuss only a single locative case/medium (adhikaraṇa or adhikarana) called ‘akṣarādhikaraṇa‘ (aksharadhikarana),(akṣaramanvarantadhṛteh etc. 1.3.10-12), where Śaṅkaracarya (Shankaracharya) explains in detail the concept of brahma in the form of  akṣara, primarily as cited in the dialogue between Yajñavalkya (Yajnavalkya) and Gargī (Gargi) in Vṛhadāraṇyaka Upaniṣada (Brihadranyaka Upanishada). Gargī had asked, “Where is the firmament all pervasive?” Yajñavalkya had replied, “What you have asked has been defined by scholars as ‘akṣara‘.” Then Yajñavalkya, to elucidate on the true nature of ‘akṣara‘, expounded on the true nature of brahma,”This thing called akṣara is neither corpulent, nor lean. Neither is it short, nor long. It is not carmine; neither does it have moisture in it. It casts neither shadow nor darkness. It is not the wind, nor the sky. It is not enamoured by anything; it is not a flavour or an essence; it is not an eye or an ear. It is not speech, nor the heart. It is not energy, nor life, and neither does it have a face. It cannot be measured, and it does not have an exterior or interior. The thing called akṣara cannot be consumed, and neither does it consume anything.”

sa hobācaitadvai tadakṣaraṃ gārgi brāhmaṇā abhibadantyasthūlamanaṇvahrasvamadīrghamalohitamasnehamacchāyamatamo’vāyunākāśamasaṅgamarasamagandhamacakṣuṣkamaśrotramabāgamano’tejaskamaprāṇamamukhamamātramanantaramabāhyam, na tadaśnāti kiñcana na tadaśnāti kaścana.

etasya vā akṣarasya praṣāsane gargi

sūryācandramasau bidhṛtau tiṣṭhataḥ,

etasya vā akṣarasya praṣāsane gargi

dyāvāpṛthibyau bidhṛte tiṣṭhataḥ.

etasya vā akṣarasya praṣāsane gargi nimeṣā

muhūrttā ahorātrāṇyarddhamāsā māsā ṛtavaḥ

saṃvatsarā iti vidhṛtāstiṣṭhantyetasya vā

akṣarasya praśāsane gargi prācyo’nyā nadyaḥ

syandante śvetebhyaḥ parbvatebhya, pratīcyo’nyā

yāṃ yāñca diśamanvetasya vā akṣarasya praśāsane

gārgi dadato manuṣyāh praśaṃsanti, yajamānaṃ

devāḥ, darbvīṃ pitaro’nvāyattaḥ.

yovā etadakṣaraṃ gārgyaviditvā’smṁilloke

juhoti yajate tapastapyate bahūni

barṣasahasrāṇyantavadevāsya tadbhavati, yo vā

etadakṣaraṃ gargyaviditvāsmāllokāt praiti,

sa kṛpaṇo’tha ya etadakṣaraṃ gārgi

viditvā-smāllokāt praiti sa brāhmaṇaḥ.

tadvā etadakṣaraṃ gārgyadṛṣṭaṃ draṣtraśrutaṃ

śrotramataṃ mantravijñataṃ vijñātṛ,

nānyadato’sti draṣṭṛ nānyadato’sti śrotṛ

nānyadato’sti mantṛ nānyadato’sti

vijñātṛ etasminnu khalvakṣare gārgyākāśa otaśca protaśceti.

There are certain ślokas (shlokas)which prove that akṣara primarily connotes brahma. There it is said that since akṣara is something that is antithetical to kṣara, or perishable substances, it is used to signify brahma. Kṣara denotes decomposable objects that are subject to cause and effect, and those that can be expressed by words and sentences. Those which lie beyond the purview of evidence that are perceptible by the senses, fall under akṣara  theory. Without learning this akṣara theory, one cannot acquire knowledge, and the state of being a true brāhmaṇa (brahmana) is achieved only after apprehending the true form of akṣara—

kṣarād viruddhadharmatvād akṣaraṃ brahma bhaṇyate;

kārya-kāraṇa-rūpaṃ tu naśvaraṃ kṣara ucyate.

yat kiñcidvastu loke’smin vāco

gocaratāṃ gatam;

pramāṇasya ca tatsarvamakṣare pratiṣidhyate.

yadaprabodhāt kārpaṇyaṃ brāhmaṇyaṃ yatprabodhataḥ

tadakṣaraṃ praboddhavyaṃ yathokteśvaravartmanā.

[As captured by Śabdakalpadruma]

Mahābhārata has mentioned the word akṣara many times, and has spoken about akṣara theory in brief. “Akṣara is one and indivisible, He is everlasting. Kṣara indicates plurality and impermanence”—

ekatvamakṣaraṃ prāhu rnānātvaṃ kṣara ucyate.

And Bhagavadgītā has said, “Akṣara is practically the Supreme brahma”—akṣaraṃ brahma paramam (8.3).