In course of life there are some observable duties, that are called are Ācāra (Achara). We do not make these codes by ourselves, which are considered as duties and advised to perform by honest, good and great men, those are called Ācāra. Those are positive and having good significance and therefore they are called sadācāra (sadachara)–
ācāra lakṣaṇo dharmaḥ santaścritralakṣaṇāḥ
sādhūnāñca ṁyathā vṛttaṃ etadācāralakṣaṇam.

It is further said in Mahābhārata (Mahabharata)– sadācāra (sadachara, good customs),  rules prescribed in Smṛtiśāstra (Smritisastra) and the Veda — these three are characteristic of dharma —
sadācāra smṛtirvedastribidhaṃ dharmalakṣaṇam.
Manu considers Ācāra to be practised customs and usages. As Manu has written — Ācāra (Achara) is the ultimate religion, and that dharma is the performance of customs as prescribed in Smṛti (Smriti) and Śruti (Sruti)–
 ācāraḥ paramo dharmaḥ śrutyuktaḥ smārta eva ca.

In fact, Ācāra is created out of the human tendency to perform some good work, since when TaittirīyaUpaniṣad (Taittiriya Upanishad) said —
satyaṃ vada dharmaṃ cara
Then a religious custom comes from this commanding word ‘cara’ and this religion is not a communal one. To speak the truth, not to be malicious –these general virtues are treated as religion. After this Upaniṣad also said — works which are flawless and unblemished, are to be done, not otherwise. We have to perform the good-natured  and virtuous works, not of other kinds.

Immediately after this, Upaniṣad (Upanishad) said — works those are faultless, unblemished, only those are to be done, not differently. We have to perform good and virtuous practices, not otherwise. In this advice of Taittirīya Upaniṣad (Taittiriya Upanishad), we find that the performance of ācāra or performable duties are included. Successive actions of great men are Sadācāra. Manu explained this thought — Seeing that — through the performance of customs the fruit/result of religion is availed /obtained — the sages concluded Ācāra as the root of all austerities.

sarvasya tapaso mūlaṃ ācāraṃṃ jagṛhuḥ param.

Works that were called Ācāra by Manu, as depicted in Śruti-Smṛti, are referred to as dharma, as mentioned in Veda and Śāstra,  and Mahābhārata called them as mentioned in , and actions introduced by saints are called Śiṣṭācīrṇa in polished language.–

tataḥ sa dharmaṃ vedoktaṃ tathā śāstroktameva ca
śiṣṭācīrṇañca dharmañca trividhaṃ cintya cetasā.
The same is narrated in Umā-Maheśvara saṃvāda in Anuśāsanaparva (Anusasanaparva) of Mahābhārata and inevitably an identical resonance is heard in Purāṇa also.

It is to say Ācāra as per Śruti or Veda is Sandhyāvandanā, Agnihotra, and the sacrifices like Jyotiṣṭoma etc. and so to say Smti — from Aśṭaka-śrāddha to various rituals according to varṇāśrama.

After these two other important things are Śiṣṭācāra, Sadācāraā and even Lokācāra. The matter of Śiṣṭācāra and Sadācāra had been so important that the discipline of Śruti-Smṛti was secondary in most of the time.

In a course of judgement in Madras High Court with reference to the context of Ācāra a citation was presented from William Jones’ translation of Manusmṛti in this way – ‘Immemorial custom is transcental Law ‘ and it was explained as — Under the Hindu system of law clear proof of usage will outweigh the written text of the law. How much importance of Śiṣṭācāra that is comprehened from the citation of Vaśiṣṭha Dharmastra. There it is said — what is prescribed in Smti-Śruti that is religion; where there is no direction in Veda or Smṛti in some special cases Śiṣṭācāra is the authority/precedent. And they are the Śiṣṭa (educated), Sādhu saint) and Sat (honest) who are akāmātmā and not selfish.

In a course of judgement in Madras High Court with reference to the context of Ācāra a citation was presented from William Jones’ translation of Manusmṛti in this way – ‘Immemorial custom is transcental Law ‘ and it was explained as — Under the Hindu system of law clear proof of usage will outweigh the written text of the law. How much importance of Śiṣṭācāra that is comprehened from the citation of Vaśiṣṭha Dharmastra. There it is said — what is prescribed in Smti-Śruti that is religion; where there is no direction in Veda or Smṛti in some special cases Śiṣṭācāra is the authority/.precedent.And they are the Śiṣṭa (educated), Sādhu (saint) and Sat (honest) who are akāmātmā (without desire in heart) and not svārthapara (selfish), who are averse to fulfill the worldly desires —
Śruti-smṛtivihito dharmaḥ

tadabhāve iṣṭācāraḥ pramāṇam .
śiṣṭṝaḥ punarakāmātmā.

Mahābhārata declared — who have good character, they are saint. Their actions/doings are the mark of śiṣṭācāra —

sādhabaḥ śīlasampannāāḥ śiṣṭācārasya lakṣaṇam/

But these greatmen were not always akāmātmā inthe verdict of śāstras. In fact the rules those wre not clearly clssified e.g. behaviour to the śūdras pratiloma vivāha and many things of varṇāśramācāras those initially were not directed in śāstras those are also in connection of śiṣṭācāra made entry subsequently into the books of Dharmaśāstras. and Brāhmaṇasṇthere were not akāmātmā,.their social interests have made there way.
In respect Ācāra it is said that deśācāra, kulācāra, even in regards of marriage strī-ācāra too have captured their places in performable duties almost inavitably . Scholars commented — marriage with the daughter of metarnal uncle is prohibited by northern preceptors, but southern civilians permted that. In this way Lokācāra has received the respect of religion irrespective of deśa (country), grāma (village) and vaṃśa (race/heredity). Who followed the rites and rituals as prescribed by Veda and other śāstras, the wre called Ārya, whoere engaged/involved in
abominable practice they ere called Anāya —
vṛttena hi bhavatyāyo na dhanena nacejyayā.

Āryatva and Anāryatva were settled upon good practice and evil deeds, not on the account of translation of ‘Ariyan’ and ‘Non-Ariyan’

anāryatvamanācāraḥ.