How does Sonadanda's characterization of a Brahmin agree or disagree with other definitions in scripture?

Question

http://www.sacred-texts.com/bud/dob/dob-04tx.htm

Dialog between Sonadanda the Brahmin and the Buddha:

" 11. Now the Blessed One became aware in his own mind of the hesitation in the mind of Sonadanda, and he thought: 'This Sonadanda is afflicted in his heart. I had better question him on his own doctrine.' And he said to him: 'What are the things, Brahman, which the Brahmans say a man ought to have in order to be a Brahman, so that if he says: "I am a Brahman," he speaks accurately and does not become guilty of falsehood?' "

.....................

" 13. And drawing his body up erect, and looking round on the assembly, he said to the Blessed One: 'The Brahmans, Gotama, declare him to be a Brahman who can accurately say "I am a Brahman" without being guilty of falsehood, who has five things. And what are the five? In the first place, Sir, a Brahman is well born on both sides, on the mother's side and on the father's side, of pure descent back through seven generations, with no slur put upon him, and no reproach, in respect of birth--

'Then he is a repeater (of the sacred words), knowing the mystic verses by heart, one who has mastered the Three Vedas, with the indices, the ritual, the phonology, and the exegesis (as a fourth), and the legends as a fifth, learned in the phrases and in the grammar, versed in Lokâyata sophistry, and in the theory of the signs on the body of a great man--

'Then he is handsome, pleasant to look upon, inspiring trust, gifted with great beauty of complexion, fair in colour, fine in presence, stately to behold,--

'Then he is virtuous, increased in virtue, gifted with virtue that has grown great--

'Then he is learned and wise, the first, or it may be the second, among those who hold out the ladle{1}.'

"

They have a dialog in which Sonadanda drops all but two requirements:

" 14. 'But of these five things, oh Brahman, is it possible to leave one out, and to declare the man who has the other four to be a Brahman, to be one who can accurately, and without falling into falsehood, claim to be a Brahman?'

'Yes, Gotama, that can be done. We could leave out colour{2}. For what does colour matter? [121] If he have the other four--good birth, technical training, virtue, and wisdom, as just set forth{3}-Brahmans would still declare him to be a Brahman; and he could rightly, without danger of falsehood, claim to be one.'

15. 'But of these four things, oh Brahman, is it possible to leave one out, and to declare the man who has the other three to be a Brahman, to be one who can rightly, and without falling into falsehood, claim to be a Brahman?'

'Yes, Gotama, that could be done. We could leave out the verses. For what do the verses matter? If he have the other three--good birth, virtue, and wisdom--Brahmans would still declare him to be a Brahman; and he could rightly, without danger of falsehood, claim to be one.'

16. 'But of these three things, Brahman, is it possible to leave one out, and to declare the man who has the other two to be a Brahman, to be one who can accurately, and without falling into falsehood, claim to be a Brahman?'

'Yes, Gotama, that could be done. We could leave out birth. For what does birth matter? If he have the other two--virtue and wisdom--Brahmans would still declare him to be a Brahman; and he could rightly, without danger of falsehood, claim to be one.'

"

Answer 1

Birth is taken into account in Hindu scriptures. Because disregarding birth means not counting the previous birth Karmas that led to this particular birth.

For example:

Manu Smriti 10.3. On account of his pre-eminence, on account of the superiority of his origin, on account of his observance of (particular) restrictive rules, and on account of his particular sanctification the Brahmana is the lord of (all) castes (varna).

So, here birth, conduct and Samskaras are all taken into account.

But, some scriptures say "Anyone who knows the Brahman is a Brahmin" and this definition is independent of birth.

Further support for Sonadanda's definition of Brahmin can be found in the following passage. It is from the last chapter of a minor Upanishad called Vajrasuchi Upanishad (this Upanishad is linked to the Samaveda):

To begin with : is jiva the brahmana ? No. Since the jiva is the same in the many past and future bodies (of all persons), and since the jiva is the same in all of the many bodies obtained through the force of karma, therefore jiva is not the brahmana. Then is the body the brahmana ? No. Since the body, as it is made up of the five elements, is the same for all people down to chandalas, 2 etc., since old age and death, dharma and adharma are found to be common to them all, since there is no absolute distinction that the brahmanas are whitecoloured, the kshatriyas red, the vais yas yellow, and the s udras dark, and since in burning the corpse of his father, etc., the stain of the murder of a brahmana, etc., will accrue to the son, etc., therefore the body is not the brahmana.

Then is a class the brahmana ? No. Since many great Rshis have sprung from other castes and orders of creation Rshyasrnga was born of deer ; Kausika, of Kusa grass ; Jambuka of a jackal ; Valmiki of valmlka (an ant-hill) ; Vyasa of a fisher man s daughter; Gautama, of the posteriors of a hare ; Vasishtha of Urvas i x ; and Agastya of a water-pot ; thus have we heard. Of these, many Rshis outside the caste even have stood first among the teachers of divine Wisdom ; therefore a class is not the brahmana. Is jnana the brahmana ? No. Since there were many kshatriyas and others well versed in the cognition of divine Truth, therefore jnana is not the brahmana. Then is karma the brahmana? No. Since the prarabdha2 , sanchita3 , and agami* karmas are the same for all beings, and since all people perform their actions as impelled by karma, therefore karma is not the brahmana. Then is a doer of dharma (virtuous actions) the brahmana ? No. Since there are many kshatriyas, etc., who are givers of gold, therefore a doer of virtuous actions is not the brahmana. Who indeed then is brahmana ? Whoever he may be, he who has directly realised his Atina and who is directly cogni zant, like the myrobalan in his palm, of his Atma that is with out a second, that is devoid of class and actions, that is free from the faults of the six stains5 and the six changes, 6 that is of the nature of truth, knowledge, bliss, and eternity, that is without any change in itself, that is the substratum of all the kalpas, that exists penetrating all things that pervades every thing within and without as akas , that is of nature of undivided bliss, that cannot be reasoned about and that is known only by direct cognition. He who by the reason of having obtained his wishes is devoid of the faults of thirst after worldly objects and passions, who is the possessor of the qualifications beginning with s ama1 , who is free from emotion, malice, thirst after world ly objects, desire, delusion, etc., whose mind is untouched by pride, egoism, etc., who possesses all these qualities and means he only is the brahmana. Such is the opinion of the vedas, the smrtis, the itihasa and the puranas. Otherwise one cannot obtain the status of a brahmana.