The Sanskrit verbal system is very complex, with verbs inflecting for different combinations of tense, aspect, mood, number, and person. Participial forms are also extensively used.
Classification of verbs
There are two broad ways of classifying Sanskrit verbal roots. They are: Parasmaipadi and Atmanepadi. But some roots are Ubhayapadi i.e. they are declined as Parasmaipadi as well as Atmanepadi roots.
Based on how the present stem is generated from the verb root, Sanskrit has ten classes (or gaṇas) of verbs divided into in two broad groups: athematic and thematic. The thematic verbs are so called because an अ(a), called the theme vowel, is inserted between the stem and the ending. This serves to make the thematic verbs generally more regular. Exponents used in verb conjugation include prefixes, suffixes, infixes, and reduplication. Every root has (not necessarily all distinct) zero, guṇa, and vṛddhi grades. If V is the vowel of the zero grade, the guṇa-grade vowel is traditionally thought of as a + V, and the vṛddhi-grade vowel as ā + V.
Seṭ and aniṭ roots
Sanskrit roots may also be classified, independent of their gaṇa, into three groups, depending on whether they take the vowel (i)इ before certain tense markers. Since the term used for this vowel by Sanskrit grammarians is (iṭ)इट्, these two groups are called सेट् (seṭ, with (स) iṭ(इट्), veṭ (optional iṭ) and अनिट् (aniṭ,without (न ~ अन्) iṭ) respectively.
The verbs tenses (a very inexact application of the word, since more distinctions than simply tense are expressed) are organized into four 'systems' (as well as gerunds and infinitives, and such creatures as intensives/frequentatives, desideratives, causatives, and benedictives derived from more basic forms) based on the different stem forms (derived from verbal roots) used in conjugation. There are four tense systems:
- Present (Present, Imperfect, Imperative, Optative)
- Future (Future, Conditional)
The present system includes the present tense, the imperfect, and the optative and imperative moods, as well as some of the remnant forms of the old subjunctive. The tense stem of the present system is formed in various ways. The numbers are the native grammarians' numbers for these classes.
For athematic verbs, the present tense stem may be formed through:
- 2) No modification at all, for example ad from ad 'eat'.
- 3) Reduplication prefixed to the root, for example juhu from hu 'sacrifice'.
- 7) Infixion of na or n before the final root consonant (with appropriate sandhi changes), for example rundh or ruṇadh from rudh 'obstruct'.
- 5) Suffixation of nu (guṇa form no), for example sunu from su 'press out'.
- 8) Suffixation of u (guṇa form o), for example tanu from tan 'stretch'. For modern linguistic purposes it is better treated as a subclass of the 5th. tanu derives from tnnu, which is zero-grade for *tannu, because in the Proto-Indo-European language [m] and [n] could be vowels, which in Sanskrit (and Greek) change to [a]. Most members of the 8th class arose this way; kar = "make", "do" was 5th class in Vedic (krnoti = "he makes"), but shifted to the 8th class in Classical Sanskrit (karoti = "he makes")
- 9) Suffixation of nā (zero-grade nī or n), for example krīṇa or krīṇī from krī 'buy'.
For thematic verbs, the present tense stem may be formed through:
- 1) Suffixation of the thematic vowel a with guṇa strengthening, for example, bháva from bhū 'be'.
- 6) Suffixation of the thematic vowel a with a shift of accent to this vowel, for example tudá from tud 'thrust'.
- 4) Suffixation of ya, for example dī́vya from div 'play'.
The tenth class described by native grammarians refers to a process which is derivational in nature, and thus not a true tense-stem formation. It is formed by suffixation of ya with guṇa strengthening and lengthening of the root's last vowel, for example bhāvaya from bhū 'be'.
The perfect system includes only the perfect. The stem is formed with reduplication as with the present system.
The perfect system also produces separate "strong" and "weak" forms of the verb — the strong form is used with the singular active, and the weak form with the rest.
The aorist system includes aorist proper (with past indicative meaning, e.g. abhūḥ "you were") and some of the forms of the ancient injunctive (used almost exclusively with mā in prohibitions, e.g. mā bhūḥ "don't be"). The principal distinction of the two is presence/absence of an augment – a- prefixed to the stem.
The aorist system stem actually has three different formations: the simple aorist, the reduplicating aorist (semantically related to the causative verb), and the sibilant aorist. The simple aorist is taken directly from the root stem (e.g. bhū-: a-bhū-t "he was"). The reduplicating aorist involves reduplication as well as vowel reduction of the stem. The sibilant aorist is formed with the suffixation of s to the stem.
The future system is formed with the suffixation of sya or iṣya and guṇa. It includes a conditional, formed from the future stem as the imperfect is formed from a thematic present stem. Rarely used in Classical Sanskrit, the conditional refers to hypothetical actions.
Sanskrit also makes extensive use of participles.
Past participles are formed directly from verbal roots for most verbs (except for verbs of the tenth gaṇa, which form them from the present stem). They have a perfective sense, in that they refer to actions that are completed. They can freely substitute for finite verbs conjugated in the past sense.
Past passive participles
The past passive participle in Sanskrit ("ktănta") is formed by placing ta at the end of the root, in certain cases preceded by an "i" vowel. For several verbs, the root itself is also modified. For instance, the root "vac", to speak, forms the past participle ukta.
Past active participles
These are regularly formed by suffixing -vant to the past passive participles. They modify the subject of the verb from which they are formed.
Unlike the past participles, the present participle is formed from the present stem of the verb, and is formed differently depending on whether the verb is parasmaipada or ătmanepada. The present participle can never substitute for a finite verb. It is also inherently imperfective, indicating an action that is still in process at the time of the main verb.
Formed from the future stem just as the present participle is formed from the present stem, the future participle describes an action that has not yet happened, but that may in the future.
The gerundive is a future passive prescriptive participle, indicating that the word modified should or ought to be the object of the action of the participle.
The perfect participle is a past active participle, but is very rarely used in classical Sanskrit.
The aorist participle used in Vedic was lost in Classical Sanskrit.
The following table is a partial listing of the major verbal forms that can be generated from a single root. Not all roots can take all forms; some roots are often confined to particular stems. The verbal forms listed here are all in the third person singular, and they can all be conjugated in three persons and three numbers.
Root: bhū-, a class I thematic verb root.
Present stem: bhava-
Passive stem: bhūya-
Future stem: bhaviṣya-
|bubhūṣati||bobhoti / bobhavīti|
|bubhūṣatu||bobhotu / bobhavītu|
|Perfect||babhūva||bhāvayām āsa||bubhūṣām āsa|
|Benedictive / precative||bhūyāt|
Taking into account the fact that the participial forms each decline in seven cases in three numbers across three genders, and the fact that the verbs each conjugate in three persons in three numbers, the primary, causative, and desiderative stems for this root when counted together have over a thousand forms.