Yajna is offering something to the gods with the help of mantras.
What is offered is less important. It could be purodasha the cake,ajyam the ghee, charu the cooked grains, pashu the animal, the somajuice, milk etc.
Yajna, yaga and ishti are synonyms.
The three varnas, brhmanas, kshatriyas and vaisyas can perform yajnas. Sometimes bahuyajamana yajnas are jointly performed by brahmanas and kshatriyas.
Sudras can not perform yajna. A married woman can participate in yajna. A sudra woman even if married to a brahmana can not participate in yajna. Cripples, eunuchs and people ignorant of Veda can not perform yajna. There are occasions where exemptions are given to some classes of sudras to be present during the yajna such as rathakara (charioteer).
The yajna is essentially performed by one who has finished his study of Veda and is married. If a brahmachari is performing a certain yajna which is allowed for him, then sacred fire is not used, purodasha is cooked on earth and not in jars and also ahutis of tongue etc. from the animal is offered in water and not in fire.
The yajna called darsapoornmasu performed on all new moon and full moon days is prescribed by Rigveda and Yajurveda. The daily agnihotra is prescribed by Yajurveda. Agnishtoma is prescribed by all Vedas.
Rigveda and Samaveda mantras are chanted aloud. Yajurveda mantras are murmured except when they are questions, replies, selecting,dialogues and commands. If the particular Yajurveda mantra is also present in Rigveda or Samaveda then it is chanted aloud.
Samidheni mantras used while lighting the agni are chanted at a volume neither high nor low.
The darsapurnamasa requires four priests, chaturmasya requires five, pasu bandha or animal sacrifice six and agnishtoma sixteen.
The Hota priest is a Rigvedi, the udgata a Samavedi, the adhvaryu a Yajurvedi and the brahma(supervisor) should know all four Vedas. Even though yajnas can be performed for kshatriyas and vaisyas, the priests have to brahmanas in all cases.
The ceremony for laying of fire for sacrifices for the first time is called agnyadhana. There are three fires, garhapatya the grandfather, dakshinagni the son and aahavaniya the grandson. The agnyadhana is done for the brahmana in spring, kshatriya in summer and vaisya in winter.
When the term "juhoti" is used it is the adhvaryu who offers the oblation.
The spoon used thus is called "juhu" also sruk. If the sruk is employed elsewhere a sruva can be used in its place.
The offering is made in the aahavaniya agni.
The vessels are preserved form agnyadhana for a lifetime and burnt with the sacrificer at his death. They are to be purified at the time of each yajna.
Veda consists of mantra bhaga and brahmana bhaga. The brahmana bhaga consists of precepts, explanations and traditions.
Many of the restrictions imposed while learning and practicing Vedas cease when offering sacrifices.
Sacrificial acts are accompanied by mantras. If it is said that plants are to be cut with 14 verses, then with each verse one plant is to be cut. If it said that one has to sprinkle three times, the mantra is said only once and sprinkling done thrice. In acts involving repetitions such as pounding the mantra is chanted only once. If a mantra is to be said if one wakes up in the night, it is to be said only once and not every time one wakes up. Similarly for crossing of the river, downpour etc. In case of bad omen that repeats the mantra has to be chanted again only if some time has elapsed after the first.
One sacrificial act may be accompanied by more than one mantra.The beginning of the act and the end of the chanting of the mantra should coincide.
In case of aghaara and dhaara the beginning of the act and the mantra coincide.
In the instruction as to which mantra is to be chanted for the act if one pada is mentioned it is for one mantra, if more than a pada is mentioned it is for three mantras and if an imperfect pada of the initial mantra is quoted it is for the whole hymn.
Hotra mantras are mantras chanted by the hota and yaajamana mantras are mantras chanted by the yajamana.
If it is said that one should sacrifice with rice and barley it means with rice after rice harvest and with barley after barley harvest and not both together.
Similarly if more than one number is mentioned for the same purpose ,for example dakshina it means any of them and not everything together.
But in buying of soma, redemption and initiation if more than one is mentioned that means aggregation.
After offering anything to Rudra, Rakshas, Nirrti, Pitrus or after cutting, breaking or throwing anything or after rubbing the body, one should touch water for purification.
All priestly acts take place on the northern part of the sacrificial ground.
The priest should never turn his back to agni nor to the sacrificial ground.
All utensils such as ladles should be held towards the agni (their tip and top facing the agni).
The yajamana and his wife should sit inside of the priests. The priests should sit sideways according to seniority.
After a sacrificial utensil such as ladle is sanctified with mantra it should not be tossed around.
Sacrificial act meant for devas should be performed facing north or east and with the yajnopavita over the left shoulder and under the right hand.
Sacrificial act for the pitrus should be performed facing south and with the yajnopavita over the right shoulder and under the left hand.
The purnamasi or full moon day should be observed as a day of abstinence.
If a person does not sacrifice with soma, the principal acts for him in Amavasya are ashta kapala for agni and ekadasa or dvadasa kapala for Indraagnee. In case of one who sacrifices with soma samnayya or mixture of milk and curd takes the place of purodasha as the second principal act meaning the Aindragna offering is omitted. Even if he is not a somayaji, the aindragna is omitted if samnayya is included.
Pindapitru yajna is a pradhana act and not auxillary to amavasya.A principal act has a name of its own such as vaisvadeva, vajapeya etc.and it has reference specific to place, time or person.
Darvi homa is done with the ladle sitting and with svahakara. For each ahuti ajyam is taken seperately. In darvi homa idhma is not used except in agnihotra where two samits are given.
While juhoti is done sitting, yajati is done standing.In darvi homa one sits west of the agni either bending or not bending the right knee.
The darvi homas are - Asruta (it is a sraavaya homa), pratysruta (when offered with sroushat), Anuvakya (when deity is invited), Yajya (accompanying the sacrifice), Upastarana (spreading for thehomadravya) and abhigharana (sprinkling of the homa dravya).
In ahutis the pouring out is done when the vashatkara is pronounced or at the end of it.
Svaha, Svadha, Vashat, Vaushat and Sraushat are the five sacrificial injunctions. Vashat us uttered by the hota.
When soma is offered it is poured out with upayama griheetosi.
When bricks are put together to make the vedi, the act starts with the starting of the hymn and ends with the end of the hymn.
When the purodasha is divided into pieces "vyavartadhvam" is used and for the last two pieces "vyavatetham".
Each piece is of the breadth of a thumb and a ladle full of the same size in case of samnayya which is liquid. When there are more number of charus and purodashas they are marked for each deity with "idam" (eg:- idam agneh). This applies for division as well.
Kapala is the jar used for cooking. When it is placed in fire for cooking the verse dhrishtarasi... or dhruvosi ( male gender charu being male) is pronounced.
Cleaning of the grains etc. takes place after the kapala is put on fire.
The plant in the field is called sasya, the grain with the husk is called dhanya, the grain without the husk is called tandula and the roasted or cooked grains is called anna.
The process of cooking is called adhisrapana and the verse is used gharmosi.
The samidhenis or verses used in kindling the agni are fifteen in number in darsapurnamasa and seventeen in number in wishful ishtis and pasubandha.
The darsapurnamasa is the prakriti or nor for all ishtis. All other ishtis are vikriti or modifications of darsapurnamasa. A sacrifice which is a vikriti can become prakriti for another sacrifice.
It is also the norm for agnishomiya pasu or animal sacrifice and also savaniya.
Savaniya is the norm for aikadasianas and aikadasinas are the norms for pasuganas.
Vaisvadeva is the norm for Varunapraghasa sakamedaha and sira.
Vaisvadevika ekakapala is the norm for all ekakapalas. Ekakapala is undivided.
Vaisvadevi amiksha is the norm for all amikshas.
Vikara (modificaion) is perceived for similarity with the prakriti (norm). Charu is perceived as a vikara or purodasha, honey and water as that of ajyam and amiksha as that of samnayya.
Offerings to a single deity is considered to be a vikara of agneya, two two deities as that of agnishomeeya and multiple deities as that of aindragna.
If there is sameness of deity and offering in prakriti and vikriti , then offering prevails. If there is contradiction in substance and method of preparation, then substance prevails. If there is contradiction
regarding substance then purpose prevails.
In the vikriti there are sometimes modification of mantras depending on the sense. But in the prakriti no such modification exists.
When what is prescribed is not available then something most similar is taken. If something very much like is not available then something a little like can be taken provided it is not a forbidden item. The
substitute should be looked upon as the substituted If vrihi is substituted by nivara it should be looked upon as vrihi only and as and when vrihi becomes available that should be used.
If the measure of the dravya is insufficient manage with whatever is available.
The yajamana, agni, devata, mantra, the act and any prohibition can not be substituted.
The prakriti stops when there is a corollary, prohibition or a loss of meaning.
Agnishtoma is the prakriti of ekaha sacrifices.Dvadashaha is the prakriti of the aharganas.Gavamayana is the prakriti of Samvatsarikas.
In agnishtoma, ukthya, shodasina and atiratra which are soma sacrifices, uttara vedi is also present.
The yajamana wishes the object of his sacrifice at the beginning. If there is wish associated with any special part if the sacrifice, then the particular wish should be made at the beginning of the special part.
One should perform the agnihotra etc. as holy duty and not with any special wish.
The brahmana should offer agnihotra at the the beginning and end of the day, the darsapurnamasa at the end of each half month, the agrayana as and when the old grains are consumed and the new grains are taken, the chaturmasya at the end of the three seasons,
pasubandha or animal sacrifice at the solstices and soma yaga at the end of the year.
A brahmana will not eat new grains without performing the agrayana or will not eat meat without performing the pasubandha.
If there are fewer mantras than the number of acts, then the acts are divided between the mantras. If there are more mantras than the number of acts then let each act be performed with one mantra leaving others as optional.