Mīmāṃsā authors think that cognitions are by themselves, i.e., intrinsically valid. In other words, they are not valid because of some additional reason, but just because of the sheer fact of being unfalsified.
In order to establish this claim, Veṅkaṭanātha defeats three possible candidates as extrinsic reasons for the cognitions’ validity, namely agreement (saṃvāda, with other people’s cognitions or with one’s other cognitions), quality of the cognition’s cause and causal efficacy (arthakriyā). The latter candidate is rejected because it would lead to an infinite regress (one would need to establish the causal efficacy of the cognition of causal efficacy and so on) and because some cognitions just don’t have any causal result. The passage is as follows:
arthakriyā ca na vyāptā, aśakyārthakriyeṣv anādarapadeṣu ca pratīteṣu puruṣapravṛttyabhāvena tanmūlārthakriyābhāvāt.
Nor is the causal efficiency (arthakriyā) included (vyāp-) [in the ascertainment of a cognition’s validity], because there is no causal efficiency as the root of certain [cognitions], given that there is no human activity (pravṛtti) in the case of apprehended [cognitions] in regard to which causal efficiency (arthakriyā) is impossible and whose contents (pada) have not been taken into account (anādara). (SM ad PMS 1.1.5)
UPDATE: The translation has been updated according to the suggestion (see comments below) by Lalitālālitaḥ (for which I am extremely grateful). I am sure he is right about the general meaning, but I would have still preferred anādarapadārtheṣu or anādaraviṣayeṣu.
Yāmuna is not strictly speaking a Vedāntin, at least not in all his works. Nonetheless, the extant portion of his Saṃvitsiddhi (henceforth SSi) starts with a typically Vedānta concern, namely the exegesis of some Upaniṣadic statements, and especially of the word advaita within them.
The presence of an Upaniṣadic, and, therefore authoritative, starting point does not mean that there is no space for argumentation. By contrast, Yāmuna discusses at length various possible interpretations, so that the quotes open rather than closing the discussion. In this sense, the Upaniṣadic quotes have the same role of controversial sacrificial issues in Pūrva Mīmāṃsā: the discussion is prompted by the problem they raise. The structure of the first pages of the SSi is the same found at times in Veṅkaṭanātha’s philosophical works such as the Seśvaramīmāṃsā insofar as the opinions of several different schools are briefly examined and refuted. However, in these pages of the SSi the opponents have only one chance to speak out their opinion, the discussion does not involve a single speaker at length, and after one has been defeated, Yāmuna moves swiftly to the next one. The situation changes, even within the same SSi, once Yāmuna moves to a topic which has metaphysical and not only hermeneutical relevance, namely whether there is only one saṃvit ‘cognition’, or whether this is differentiated according to its various intentional contents. Here, the discussion turns into an engaging succession of objections and replies.
Yāmuna at times lets some space for sarcasm. An interesting case contrasts Yāmuna’s point of view to that of “believer” Vedāntins (the opponents are identified immediately before as brahmavidaḥ ‘knowers of brahman’. The context is that of the denial of any difference, so that one can postulate that these are Advaita Vedāntins):
Enough! This teaching about brahman suits [only] believers. We are not believers and resort to reason.
hanta! brahmopadeśo ’yaṃ śraddadhāneṣu śobhate. vayam aśraddadhānās ’smo ye yuktiṃ prārthayāmahe. (SSi 1942 p. 131).
(I have been asked to write a short introduction to Viśiṣṭādvaita Vedānta and would like to test it on you, dear readers. Any comment or criticism would be more than welcome!)
In its full-fledged form, the Viśiṣṭādvaita Vedānta (henceforth VV) is a Vedāntic school, thus one which accepts the authority of the Upaniṣads, the Brahmasūtra and the Bhagavadgītā and which recognises a form of God as brahman (on the various ways of understanding God in India, see here). The full-fledged VV accepts also further groups of texts, namely on the one hand the Pañcarātra (a group of Vaiṣṇava texts prescribing personal and temple rituals, see Leach 2012, and, here) and on the other the Tamil devotional poems collected in the Divyaprabandham.
(The following is my attempt to make sense of Rāmānuja’s conceptions of bhakti. Comments and criticisms are welcome!)
To Rāmānuja (traditional dates 1017–1137) are attributed, with more or less certainty, a series of Vedāntic works, namely the Śrī Bhāṣya (henceforth ŚrīBh) commentary on the Brahma Sūtra (henceforth UMS), which is his philosophical opus magnum, both in length and philosophical depth, the Gītabhāṣya on the Bhagavadgītā (henceforth BhG), a compendium of his philosophy, the Vedārthasaṅgraha, and two shorter commentaries on the UMS, namely the Vedāntadīpa and the Vedāntasāra.
Beside these works, the Viśiṣṭādvaita Vedānta school, at least since the time of Sudarśana Sūri and Veṅkaṭanātha (also called Vedānta Deśika, traditional dates 1269–1370), recognised Rāmānuja as the author of also three extremely short works (about 3–4 pages each), namely the Śaraṇāgatigadya, the Śrīraṅgagadya and the Vaikuṇṭhagadya, and of a manual of daily worship called Nityagrantha.
The terms bhakti `devotional love’ and bhakta `devotee’ are not very frequent in the ŚrīBh, where they are mentioned slightly more than ten times, a portion of which in quotes (some of which from the BhG). By contrast, the Śaraṇāgatigadya mentions bhakti 19 times in its only 23 sentences, and adds further elements to it (such as Nārāyaṇa instead of Kṛṣṇa as the object of devotion, and the role of prapatti ‘self-surrender’, see immediately below). Does this mean that the Śaraṇāgatigadya is not by Rāmānuja and represents a further stage in the theological thought of Viśiṣṭādvaita Vedānta? Alternatively, one might suggest that Rāmānuja addressed different audiences in his philosophical and in his religious works. In other words, the difference between the position of the ŚrīBh and that of the Śaraṇāgatigadya could be only due to the fact that the first develops a philosophical discourse about God, whereas the latter enacts the author’s relationship with Him.