There are a lot of theories regarding the oneness of the Supreme Being and the unitary character of Sri and Vishnu. The main question that is raised here is that if Sri is vibhu and is on par with Vishnu, would it not amount to admitting two deities as the Ruler of the universe. On the face of it, it appears to be a sound and valid objection. But when we understand correctly the sense in which the Divine couple is described as constituting one Reality (para-tattva) it becomes untenable. There are two explanations for upholding the idea that the Divine couple together constitutes the paratattva. The first is a philosophical. It is based on the metaphysical concept of substance and attribute and the theory of aprathaksiddhi or the concept of inseparability admitted in the Visistadvaita Vedanta, to explain the oneness of Brahman as a visista entity. The second is a theological justification based on the logical principle of vyasajya vritti, the Naiyayika concept according to which a common quality can belong to two entities.

Philosophical Justification for Unitary Character of Sri and Vishnu
Regarding the first point, the Visistadvaita metaphysics maintains that the substance and attribute are distinct but they are inherently related. By virtue of the inherent relationship, the substance as qualified by the attribute is one entity. This is the concept of visista or substance as integrally related to its attribute.

On the basis of this principle, Ramanuja has formulated the organic relationship between Ishwara and the universe of cit and acit. The ultimate Reality of Visistadvaita Vedanta is Brahman as organically related to cit and acit (cid-acit-visista Brahma). Though the three ontological entities are distinct by virtue of their intrinsic nature, Brahman as a visista entity is one even though associated with cit and acit. Further, according to the Visistadvaita Vedanta Brahman is satya or absolute reality, jnana or infinite knowledge and ananta or infinite. All the three terms represent the essential characteristics or asadharana dharmas of Brahman. Each one is a distinctive dharma and it is also different from the substrate (Brahma svarupa) in which it inheres. In epistemological terms the essential characteristics of an entity are integrally related to the svarupa. The two are aprthaksiddha or inseparable. Brahman and the essential attributes, though distinct as dharmi and dharma, Brahman as characterised by the attributes is one entity. This is the fundamental concept of Reality in Visistadvaita as expounded by Ramanuja, which is acceptable to all his followers.

The concept of Goddess Sri as an integral part of Brahman is to be understood on the basis of the same metaphysical principle. Sri is admitted in Vaishnavism as an asadharana-dharma or as a unique characteristic of Vishnu in so far as She serves as an identity mark to distinguish Vishnu from other Vedic deities.

The Purusa sukta of the Rig Veda provides the basis for holding this theory. The first part of the Purusa sukta speaks of the ultimate Reality as Purusa. In order to determine the name of the particular Vedic deity to which the general term Purusa is applicable, the statement found in the uttaranuvaka or the later passage of Purusa sukta in which Sri is specifically mentioned as patni, is adopted as the criteria for deciding the fact that Purusa is Sriyah pati and that He is the ultimate Reality and not any other deity such as Brahma, Rudra etc. In view of this the qualification, viz., sriyah patitva is taken by the Vaishnava acharyas as asadharana-dharma or distinguishing characteristic.

The Pancharatra Samhitas have conceived Goddess Lakshmi in terms of sakti of Vishnu. In other words, though God and Goddess as two sentient beings are distinct deities; they are regarded as constituting one Reality in terms of the integral relationship. As an integral part of Vishnu, Goddess Sri possesses all the characteristics of Narayana such as svarupa, rupa, gurta, vibhava etc. as Ramanuja has stated.

In view of these explanations, the question whether Sri is vibhu is not relevant. As an integral part of Vishnu, She cannot be anything but infinite (vibhu) in character as the Vishnu purana states (sarvagatah). The question whether She is a giver of moksa also does not arise. As part of Vishnu, She has the capacity to grant moksa. This fact is also clearly stated in the Vishnu Purana, as a part of the ultimate Reality, Goddess also partakes in the major cosmic functions of creation, sustenance and dissolution, as the Pancaratra Samhitas point out.

The admission of Sri on par with Vishnu does not also militate against Her major role as an interceder (purusakaratva) in addition to Her other divine functions. As a feminine deity, purusakaratva is undoubtedly an important characteristic of Sri, like the other unique motherly qualities such as vatsalya or loving disposition and compassion or daya. But these qualities including Her role as mediator should not lower Her ontological status. As explained by Parasara Bhattar, the division of certain specific roles between the Lord and His consort, is by mutual agreement and as such it does not either enhance the greatness of the one against the other or lower the status of one as against the other.79 What is arranged by one's own will (ichha) by mutual agreement would not affect the ontological status of the divine couple.

Theological Justification for Unitary Character of Sri and Vishnu
It may be noted that Goddess in Vaishnavism is not conceived as an independent deity but on the contrary, She is regarded as a dependent Reality. Lakshmi Tantra and Ahirbudhanya Samhita which discuss the doctrine of Goddess present the same picture. Nowhere in the Vaishnava religious literature, is Lakshmi taken as an absolutely independent tattva, unlike in Saktaism. As a dependent Reality, inseparably related to God, the unitary character of Ishwara as one visista-tattva (Reality) is not affected in the same way as Brahman even though organically related to the universe of cit and acit remains non-dual.

The fact that Goddess is sesa bhuta or a dependent deity does not affect Her parity with Vishnu and Her being the Sovereign of the universe for two reasons. In the first place, She is not included in the category of individual souls, because there are no scriptural and Smriti statements affirming explicitly that She is monadic in character and belongs to the jiva koti. On the contrary, there is sufficient justification to regard Her as part of Ishwara.

Secondly, the sesatva or the dependent character of Sri is assumed by Her voluntarily out of Her own will with the mutual agreement between the Lord and Herself. As a consort (patni) of the Supreme Lord, She has chosen to remain sesa bhuta to the latter presumably out of respect for the Lord. The assumption of a specific characteristic like sesatva out of one's free will does not affect the intrinsic nature of Her Sovereignty.

The implication of all these statements is that Goddess Sri is Sesi or Ruler for the entire universe excluding Her Lord; whereas God is the Ruler of all including His consort. In other words, both God and Goddess are Sesi or the Sovereign of the universe except one difference, viz., that the former is the Ruler of all including Goddess, whereas the latter is Ruler of all except God (ekona sesi). As Isvari of the entire universe of cit and acit, She enjoys a higher ontological status than the individual souls (jivas) which are by their very intrinsic nature absolutely dependent beings (ninipadhika-sesatva). As distinct from individual souls and as sovereign of the universe She is at par with Vishnu.

There is no contradiction involved in two ontological entities which are on par in every respect having a common function of the Lordship of the universe (isitrtva). Such a concept of two-in-one is not logically untenable. In Indian Logic, we speak of the concept of vyasyajya-vrtti, which means that a single property or quality belongs to two. Thus, for instance, the concept of relation inheres in both the relata (ubhctya-nistd). In the same way, sesitva can be applicable to both the deities.

It is in this sense that we should understand the theory of God and Goddess together constituting one para tattva and not in the sense of tadatmya or absolute identity which is philosophically unacceptable. Keeping this truth in mind Sriramamisra popularly known as Somasi Andan, who is one of the pupils of Ramanuja describes para tattva of Vaisnavism in the following terms: ubhayddhistdnam ca ekam sesitvam. The meaning of it is that lesitva or Lordship which is one inheres in, both. That is, sesitva does not exclusively belong to tile Supreme Lord but it equally applies to Goddess Lakshmi. In other words, the Divine couple (divya-dampati) are the sovereign of the universe.