The word bhakti comes from the root bhaj, which means to serve.  Therefore, the primary meaning of the word bhakti is to render service.  Sri Rupa Gosvami1 has described the intrinsic characteristics of bhakti in Sri Bhakti-rasamrta-sindhu (1.1.11) as follows:  

“Uttama-bhakti, pure devotional service, is the cultivation of activities that are meant exclusively for the benefit of Sri Krishna, in other words, the uninterrupted flow of service to Sri Krishna, performed through all endeavors of body, mind, and speech, and through expression of various spiritual sentiments (bhavas).  It is not covered by jnana, (knowledge of nirvisesa-brahma, aimed at impersonal liberation), and karm,a (reward-seeking activity), yoga or austerities; and it is completely free from all desires other than the aspiration to bring happiness to Sri Krishna.”  

Is This Question Important? 

Before debating whether bhakti, can be called a science, perhaps we need to decide if the question is important.  Science and religion have different focal points.   

• Religion is about values and moral judgments.   
• Science is about understanding how nature works, and using those discoveries in a variety of ways.   

Understanding the power inherent in the atom, for example, science will harness that power, and build a bomb.  Whether to use that bomb is not a question of science, but of values, and values are the province of religion.  Therefore, science and religion, though popularly seen as competing worldviews; are in truth, mutually exclusive.   

Nevertheless, from the remote past to the present day, learned spokespersons for bhakti, have referred to it as a science, and bhakti scriptures like the Srimad Bhagavatam, and Brahma Samhita, refer to it as a science.  Subsequently, contemporary adherents to bhakti also call it a science.   The process of bhakti-yoga is not a concoction or speculation. It is a science. As stated in Srimad-bhagavatam 1.2.20, 

Thus, established in the mode of unalloyed goodness, the man whose mind has been enlivened by contact with devotional service to the Lord gains positive scientific knowledge of the Personality of Godhead in the stage of liberation from all material association.” 

It is a science. Just like in Caitanya-caritamrta2 Madhya 8.128, Caitanya Mahaprabhu3 said, 

“It does not matter whether he is a sannyasi, (person in the renounced order of life), or grhastha, (married householder), or brahmacari, (celibate student). One who knows the science of Krishna and preaches all over the world, he is guru, spiritual master. It does not matter.” 

Some people take exception to this, however, perhaps thinking that even if scripture and some religious seers refer to bhakti as a science, they must be using the term loosely.  So why perpetuate their inadvertent mistake.  Why keep calling bhakti a science and making a poor impression on those who know that religion is about values and beliefs, while science is about proven truths; why not keep the two things mutually exclusive?  

This is not a bad proposal.  It is always good to seek precision, and clarity when communicating ideas.  Nevertheless, in fairness to the bhakti scriptures, and the seers who refer to bhakti as a science, we ought to determine whether they used the term inadvertently.   

Another reason for such an investigation is that those who believe in science, finding its achievements impressive, often criticize religion.  Religion, they claim, is nothing but an irrational yearning by those who withdraw from growing up, and standing on their own two emotional feet in life.  These people lack the courage for the adventure of being; hence, they look for a father figure, God, to buffer them from life’s realities.  If these anti-religion persons are to consider religion, and if there is a scientific type of religion, as bhakti claims to be, it could be a great help to them.  After all, science needs values to guide its application.  A scientific type of religion would be the order of the day.