(READ THIS CAREFULLY IF YOU HAVE QUERY ON HOW DO WE ENSURE THAT VEDAS ARE UNALTERABLE SINCE AGES. We are thankful to several scholars whose source we could not track but whose works were used for creation of this article.)
On how Vedas have been preserved in pristine state, here are some analytical, unbiased and objective pointers. We provide here some details on how Vedas have been preserved so purely and how its not possible to alter even a single syllable. No other text in the world can claim to have such fail-safe method of preservation.
Our forefathers devised a number of methods to preserve the unwritten Vedas in their original form, to safeguard their tonal and verbal purity.

Swara Protection of Vedas

They laid down rules to make sure that not even a syllable was changed in chanting, not even a svara was altered. In this way they ensured that the full benefits were derived from intoning the mantras. They fixed the time taken to enunciate each syllable of a word and called this unit of time or time interval “matra”.
How we must regulate our breathing to produce the desired vibration in a particular part of our body so that the sound of the syllable enunciated is produced in its pure form: this science is explained in the Vedanga called Shiksha.
If you see a Vedic mantra in the Samhita, you would find certain marks after syllables. For example see the following image:

 
 
 

These marks called Swara Chinha depict the method of pronunciation. These markers ensure that not even a single syllable can be altered from any Vedic mantra.

In traditional gurukuls, pupils memorize the locations of these Swaras through specific hand or head movements. Thus you would see them moving their hands or head while reciting the Vedic mantras. And if a slightest error in Swara is found in recitation, they would easily pin-point it.

Further, different gurukuls specialize in studying different Patha methods (explained after this section) would still have the same Swara system in place, thereby easily tracking accuracy of each Vedic mantra to last syllable.

Paatha Protection of Vedas
A remarkable method was devised to make sure that words and syllables are not altered. According to this the words of a mantra are strung together in different patterns like “vakya”, “pada”, “karma”, “jata”, “mala”, “sikha”, “rekha”, “dhvaja”, “danda”, “ratha”, “ghana”. These represent different permutations of reciting words of a Vedic Mantra.
We call some Vedic scholars “ghanapathins”, don’t we? It means they have learnt the chanting of the scripture up to the advanced stage called “ghana”. “Pathin” means one who has learnt the “patha”. When we listen to ghanapathins chant the ghana, we notice that they intone a few words of a mantra in different ways, back and forth.
It is most delightful to the ear, like nectar poured into it. The sonority natural to Vedic chanting is enhanced in ghana. Similarly, in the other methods of chanting like karma, jata, sikha, mala, and so on the intonation is nothing less than stately, indeed divine.
The chief purpose of such methods, as already mentioned, is to ensure that not even a syllable of a mantra is altered to the slightest extent. The words are braided together, so to speak, and recited back and forth.
In “vakyapatha” and “samhitapatha” the mantras are chanted in the original (natural) order, with no special pattern adopted. In the vakyapatha some words of the mantras are joined together in what is called “sandhi”. There is sandhi in Tamil also; but in English the words are not joined together. You have many examples of sandhi in the Tevaram, Tiruvachakam, Tirukkural, Divyaprabandham and other Tamil works. Because of the sandhi the individual words are less recognisable in Sanskrit than even in Tamil.
In padapatha each word in a mantra is clearly separated from the next. It comes next to samhitapatha and after it is kramapatha. In this the first word of a mantra is joined to the second, the second to the third, the third to the fourth, and so on, until we come to the final word.
In old inscriptions in the South we find the names of some important people of the place concerned mentioned with the appellation “kramavittan” added to the names. “Kramavittan” is the Tamil form of “kramavid” in the same way as “Vedavittan” is of “Vedavid”. We learn from the inscriptions that such Vedic scholars were to be met throughout South India in past.
(Note that South India has a great contribution in preserving the Vedic traditions during a critical long era of history when North India was occupied in struggling for survival from brutal attacks of barbaric invaders and their progenies from West Asia. We find the tradition of Vedic gurukuls uninterrupted even till today.)
In jata patha, the first word of the mantra is chanted with the second, then the order is reversed-the second is chanted with the first. Then, again, the first word is chanted with the second, then the second with the third, and so on. In this way the entire mantra is chanted, going back and forth.
In shikhapatha the pattern consists of three words of a mantra, instead of the two of jata.
Ghanapatha is more difficult than these. There are four types in this method. Here also the words of a mantra are chanted back and forth and there is a system of permutation and combination in the chanting. To explain all of it would be like conducting a class of arithmetic.
We take all kinds of precautions in the laboratory, don’t we, to protect a life-saving drug? The sound of the Vedas guards the world against all ills. Our forefathers devised these methods of chanting to protect the sound of our scripture against change and distortion.
Samhitapatha and padapatha are called “prakrtipatha” (natural way of chanting) since the words are recited only once and in their natural order. The other methods belong to the “vikrtipatha” (artificial way of chanting) category. (In krama, though the words do not go in the strict natural order of one-two-three, there is no reversal of the words-the first after the second, the second after the third, and so on. So we cannot describe it fully as vikrtipatha). Leaving out krama, there are eight vikrti patterns and they are recounted in verse to be easily remembered.
Jata mala sikha rekha dhvaja dando ratho ghanah
Ityastau-vikrtayah proktah kramapurva maharsibhih
All these different methods of chanting are meant to ensure the tonal and verbal purity of the Vedas for all time. In pada the words in their natural order, in krama two words together, in jata the words going back and forth. The words tally in all these methods of chanting and there is the assurance that the original form will not be altered.
The benefits to be derived from the different ways of chanting are given in this verse.
Samhitapathamatrena yatphalam procyate budhaih
Padu tu dvigunam vidyat krame tu ca caturgunam
Varnakrame satagunam jatayantu sahasrakam
Considering that our ancestors took so much care to make sure that the sound of the Vedas did not undergo the slightest change, it is futile for modern researchers to try to establish the date of our scriptures by finding out how the sounds of its words have changed.
What more, today different schools of Vedas exist in south who memorize vedas in different means, as explained above. And if you compare the mantras memorized by different schools, you will find variation of not a single syllable. Remember we are talking lacs of syllables!! And still no variations. Thats why even Max Muller, a bitter critic of Vedic philosophy, could also not help but state that such a foolproof method of preservation is among the greatest wonders and miracles of the world!

An example of Ghana Patha

(Reference Source: http://www.krishnamurthys.com/profvk/index.html )
This example gives a faint glimpse of how the vedas in spite of its massive content, (Rg veda and Yajur veda have 153,826 words and 109,287 words respectively) have been preserved from generation to generation though it was all done only by oral transmission.
We give below a sentence from the Yajur veda, obviously without the svaras, in its original samhita pATha form, also its pada text and then the order of the words in the ghana recital. A pundit who has learnt the Ghana recital of one complete veda (he takes thirteen years of whole time work to reach that stage) is called a ghana-pAThi.
First we give the rule for the ghana mechanics of recitation:
If the original order of words in a sentence is:
1/2/3/4/5
The ghana recital goes as follows:
12/21/123/321/123/
23/32/234/432/234/
34/43/345/543/345/
45/54/45/
5 iti 5.

Example:

samhita sentence:
eshAm purushANAm-eshAm paSUnAM mA bher-mA ro-mo eshAM kincanAmamat //
Meaning:
Oh God! Do not frighten these our men and animals, may none of these perish or lack health.
pada text:
eshAM/purushANAM/eshAM/paSUnAM/mA/bheH/mA/arah/mo-iti-mo/eshAM/
kim/chana/Amamat/Amamad-ity-Amamat/
Note: The ninth break here and the last break are the results of a technicality which you may ignore, unless you want to specialise in this art.
Now for the ghana recital(without the svaras; with the svaras it would be a delight to hear). The recital is a non-stop recital, except for a half-pause at the place shown by / . There is no break anywhere else. The hyphens shown are for requirements of those who can decipher the grammar ; they will not be reflected in the recital.
eshAM-purushANAM-purushANAm-eshAm-eshAM purushANAm-eshAm-eshAm
purushANAm-eshAm-eshAm purushANAm-eshAM /
purushANAm-eshAm-eshAM purushANAM purushANAm-eshAM paSUnAM
paSunAm-eshAm purushANAm purushANAm-eshAM paSUnAM /
eshAM paSUnAM paSUnAm-eshAm-eshAM paSUnAm-mA mA paSUnAm-eshAm-eshAM paSUnAm-mA /
paSUnAm-mA mA paSUnAM paSUnAm-mA bher-bher-mA paSUnAM paSUnAm-mA bheH /
mA bher-bher-mAmA bher-mAmA bher-mAmA bher-mA /
bher-mAmA bher-bher-mAro aro mA bher-bhermA araH /
mA ro aro mAmA ro momo aro mA mA ro mo /
aro mo mo aro aro mo eshAm-eshAm mo aro aro mo eshAM /
mo eshAm-eshAm mo mo eshAm kim kim-eshAm-mo mo eshAm kim / mo iti mo/
eshAm kimkim-eshAmeshAM kim-cana cana kim-esham-eshaM kim-cana /
kim cana cana kim kim canAmamad-Amamat cana kim kim canAmamat /
canAmamad-Amamac-cana canAmamat /
Amamad-ityAmamat /
The significant point to note here is that in Sanskrit the order of words does not matter.
If you do it with an English sentence like:
Rama vanquished Ravana
It will go like this:
Rama vanquished vanquished Rama Rama vanquished Ravana ‘Ravana vanquished Rama’ Rama vanquished Ravana … and so on.
You can see the absurdity now. In Sanskrit this absurdity would not arise. So a ghana recitation is supposed to be equivalent to a recitation of the veda 13 times and to that extent is multifold fruitful! The 13 is because except for two beginning and two ending words in a sentence the others are repeated 13 times. (You can check it with the word paSUnAM above).

To summarize:

All the Veda Mantras have been preserved (till today) (at least three millenia according to western calculations) without ever putting them into writing. This must be considered a great lingusitic achievement of which India can be legitimately proud. The literature, which consists of diverse poetical and prose compositions were simply learnt by rote, the training being given by the teacher saying each word or combinations of words once with the proper incantations (called svaras) and the students saying it twice. They then learnt to recite it in continuous form along with the incantations. The continuous recitation of a vedic text is called samhita pAtha. The accuracy of the text is preserved by resorting to an artifice of nine different techniques or modes of recital.
The first is the pada pATha, which simply recites each word of the text separately; pada means word; pAtha means reading.The euphonic changes that occurs from the samhita pATha to the pada pATha is itself very technical (Sanskrit grammar would be crucial here) but makes sense.
In addition, there are eight other techniques of recitation, the sole purpose of each is to preserve the original samhita text without the loss or addtion of a single syllable or svara. The svaras are a significant part of the recital of the vedas, whatever be the mode. The eight modes are called:
krama, jaTa, ghana, mAlA, ratha, ShikhA, daNDa and rekhA.
In each mode the order of recital of the words is specified as a particular permutation of their original sequence.
All these elaborate and sophisticated approaches have ensured that the first texts of humanity – The Veda Samhitas – are available to us today in exactly the same pure original form.
This article is also available in Hindi at http://agniveer.com/3887/why-vedas-cannot-be-changed-hi/
This article is also available in Hindi at http://agniveer.com/3887/why-vedas-cannot-be-changed-hi/
This article is also available in Gujarati at http://agniveer.com/why-vedas-cannot-be-changed-gu/
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