Field of study
The study of interpersonal relationships involves several branches of the social sciences, including such disciplines as sociology, psychology, anthropology, and social work. Interpersonal skills are vital when trying to develop a relationship with another person. The scientific study of relationships evolved during the 1990s and came to be referred to as 'relationship science', which distinguishes itself from anecdotal evidence or pseudo-experts by basing conclusions on data and objective analysis. Interpersonal ties are also a subject in mathematical sociology.
Human beings are innately social and are shaped by their experiences with others. There are multiple perspectives to understand this inherent motivation to interact with others.
- Need to belong
According to Maslow's hierarchy of needs, humans need to feel love(sexual/nonsexual) and acceptance from social groups (family, peer groups). In fact, the need to belong is so innately ingrained that it may be strong enough to overcome physiological and safety needs, such as children's attachment to abusive parents or staying in abusive romantic relationships. Such examples illustrate the extent to which the psychobiological drive to belong is entrenched.
- Social exchange
Another way to appreciate the importance of relationships is in terms of a reward framework. This perspective suggests that individuals engage in relations that are rewarding in both tangible and intangible ways. The concept fits into a larger theory of social exchange. This theory is based on the idea that relationships develop as a result of cost-benefit analyses. Individuals seek out rewards in interactions with others and are willing to pay a cost for said rewards. In the best-case scenario, rewards will exceed costs, producing a net gain. This can lead to "shopping around" or constantly comparing alternatives to maximize the benefits (rewards) while minimizing costs.
- Relational self
Relationships are also important for their ability to help individuals develop a sense of self. The relational self is the part of an individual’s self-concept that consists of the feelings and beliefs that one has regarding oneself that develops based on interactions with others. In other words, one’s emotions and behaviors are shaped by prior relationships. Thus, relational self theory posits that prior and existing relationships influence one’s emotions and behaviors in interactions with new individuals, particularly those individuals that remind him or her of others in his or her life. Studies have shown that exposure to someone who resembles a significant other activates specific self-beliefs, changing how one thinks about oneself in the moment more so than exposure to someone who does not resemble a significant other.
Interpersonal relationships are dynamic systems that change continuously during their existence. Like living organisms, relationships have a beginning, a lifespan, and an end. They tend to grow and improve gradually, as people get to know each other and become closer emotionally, or they gradually deteriorate as people drift apart, move on with their lives and form new relationships with others. One of the most influential models of relationship development was proposed by psychologist George Levinger. This model was formulated to describe heterosexual, adult romantic relationships, but it has been applied to other kinds of interpersonal relations as well. According to the model, the natural development of a relationship follows five stages:
- Acquaintance and acquaintanceship – Becoming acquainted depends on previous relationships, physical proximity, first impressions, and a variety of other factors. If two people begin to like each other, continued interactions may lead to the next stage, but acquaintance can continue indefinitely. Another example is association.
- Buildup – During this stage, people begin to trust and care about each other. The need for intimacy, compatibility and such filtering agents as common background and goals will influence whether or not interaction continues.
- Continuation – This stage follows a mutual commitment to quite a strong and close long-term friendships, romantic relationship, or even marriage. It is generally a long, relative stable period. Nevertheless, continued growth and development will occur during this time. Mutual trust is important for sustaining the relationship.
- Deterioration – Not all relationships deteriorate, but those that do tend to show signs of trouble. Boredom, resentment, and dissatisfaction may occur, and individuals may communicate less and avoid self-disclosure. Loss of trust and betrayals may take place as the downward spiral continues, eventually ending the relationship. (Alternately, the participants may find some way to resolve the problems and reestablish trust and belief in others.)
- Termination – The final stage marks the end of the relationship, either by breakups, death, or by spatial separation for quite some time and severing all existing ties of either friendship or romantic love.
Friendships may involve some degree of transitivity. In other words, a person may become a friend of an existing friend's friend. However, if two people have a sexual relationship with the same person, they may become competitors rather than friends. Accordingly, sexual behavior with the sexual partner of a friend may damage the friendship (see love triangle). Sexual activities between two friends tend to alter that relationship, either by "taking it to the next level" or by severing it.
A list of interpersonal skills includes:
- Verbal communication – What we say and how we say it.
- Nonverbal communication – What we communicate without words, body language is an example.
- Listening skills – How we interpret both the verbal and non-verbal messages sent by others.
- Negotiation – Working with others to find a mutually agreeable outcome.
- Problem solving – Working with others to identify, define and solve problems.
- Decision making – Exploring and analysing options to make sound decisions.
- Assertiveness – Communicating our values, ideas, beliefs, opinions, needs and wants freely.
Flourishing, budding, blooming, blossoming relationships
Positive psychologists use the various terms "flourishing, budding, blooming, blossoming relationships" to describe interpersonal relationships that are not merely happy, but instead characterized by intimacy, growth, and resilience. Flourishing relationships also allow a dynamic balance between focus on the intimate relationships and focus on other social relationships.
While traditional psychologists specializing in close relationships have focused on relationship dysfunction, positive psychology argues that relationship health is not merely the absence of relationship dysfunction. Healthy relationships are built on a foundation of secure attachment and are maintained with love and purposeful positive relationship behaviors. Additionally, healthy relationships can be made to "flourish." Positive psychologists are exploring what makes existing relationships flourish and what skills can be taught to partners to enhance their existing and future personal relationships. A social skills approach posits that individuals differ in their degree of communication skill, which has implications for their relationships. Relationships in which partners possess and enact relevant communication skills are more satisfying and stable than relationships in which partners lack appropriate communication skills.
Adult attachment and attachment theory
Healthy relationships are built on a foundation of secure attachments. Adult attachment models represent an internal set of expectations and preferences regarding relationship intimacy that guide behavior. Secure adult attachment, characterized by low attachment-related avoidance and anxiety, has numerous benefits. Within the context of safe, secure attachments, people can pursue optimal human functioning and flourishing. This is because social acts that reinforce feelings of attachment also stimulate the release of neurotransmitters such as oxytocin and endorphin, which alleviate stress and create feelings of contentment. Attachment theory can also be used as a means of explaining adult relationships.
Stages of romantic interpersonal relationships can also be characterized more generally by the following: attraction; initiation; development; sustaining vs. terminating.
- Attraction – Premeditated or automatic, attraction can occur between acquaintances, coworkers, lovers, etc., be based on sexual arousal, intellectual stimulation, or respect. Studies have shown that attraction can be susceptible to influence based on context and externally induced arousal, with the caveat that participants be unaware of the source of their arousal. A study by Cantor, J. R., Bryant, J., & Zillmann, D. (1975), induced arousal through physical exercise and found that participants rated erotic pictures highly 4 min post-exercise (when no longer realized aroused by exercise) than either immediately after (when arousal and awareness were greater) or 10 minutes later (when exercise-induced arousal had dissipated). As supported by a series of studies, Zillman and colleagues showed that a preexisting state of arousal can heighten reactions to affective stimuli. A classic study by Dutton & Aron (1974) showed that fear arousal from suspension bridges leads to higher attraction ratings by males of a female confederate.
- Initiation – There are several catalysts in the initiation of a new relationship. One commonly studied factor is physical proximity (also known as propinquity). The MIT Westgate studies famously showed that greater physical proximity between incoming students in a university residential hall led to greater relationship initiation. More specifically, only 10% of those living on opposite ends of Westgate West considered each other friends while more than 40% of those living in adjacent apartments considered each other friends. The theory behind this effect is that proximity facilitates chance encounters, which lead to initiation of new relationships. This is closely related to the mere exposure effect, which states that the more an individual is exposed to a person or object, the more s/he likes it. Another important factor in the initiation of new relationships is similarity. Put simply, individuals tend to be attracted to and start new relationships with those who are similar to them. These similarities can include beliefs, rules, interests, culture, education, etc. Individuals seek relationships with like others because like others are most likely to validate shared beliefs and perspectives, thus facilitating interactions that are positive, rewarding and without conflict.
- Development – Development of interpersonal relationships can be further split into committed versus non-committed romantic relationships, which have different behavioral characteristics. In a study by Miguel & Buss (2011), men and women were found to differ in a variety of mate-retention strategies depending on whether their romantic relationships were committed or not. More committed relationships by both genders were characterized by greater resource display, appearance enhancement, love and care, and verbal signs of possession. In contrast, less committed relationships by both genders were characterized by greater jealousy induction. In terms of gender differences, men used greater resource display than women, who used more appearance enhancement as a mate-retention strategy than men.
- Sustaining vs. terminating – After a relationship has had time to develop, it enters into a phase where it will be sustained if it is not otherwise terminated. Some important qualities of strong, enduring relationships include emotional understanding and effective communication between partners. Research has also shown that idealization of one’s partner is linked to stronger interpersonal bonds. Idealization is the pattern of overestimating a romantic partner’s positive virtues or underestimating a partner’s negative faults in comparison to the partner’s own self-evaluation. In general, individuals who idealize their romantic partners tend to report higher levels of relationship satisfaction. Other research has examined the impact of joint activity on relationship quality. In particular, studies have shown that romantic partners that engage in a novel and exciting physical activity together are more likely to report higher levels of relationship satisfaction than partners that complete a mundane activity.
In his triangular theory of love, psychologist Robert Sternberg theorizes that love is a mix of three components: some (1) passion, or physical attraction; (2)intimacy, or feelings of closeness; and (3) commitment, involving the decision to initiate and sustain a relationship. The presence of all three components characterizes consummate love, the most durable type of love. In addition, the presence of intimacy and passion in marital relationships predicts marital satisfaction. Also, commitment is the best predictor of relationship satisfaction, especially in long-term relationships. Positive consequences of being in love include increased self-esteem and self-efficacy.
Referring to the emotion of love, Psychiatrist Daniel Casriel defined the “logic of love” as “the logic of pleasure and pain” in the concept of a "Relationship Road Map" that became the foundation of PAIRS' relationship education classes.
Theories and empirical research
Confucianism is a study and theory of relationships especially within hierarchies. Social harmony—the central goal of Confucianism—results in part from every individual knowing his or her place in the social order, and playing his or her part well. Particular duties arise from each person's particular situation in relation to others. The individual stands simultaneously in several different relationships with different people: as a junior in relation to parents and elders, and as a senior in relation to younger siblings, students, and others. Juniors are considered in Confucianism to owe their seniors reverence and seniors have duties of benevolence and concern toward juniors. A focus on mutuality is prevalent in East Asian cultures to this day.
The mindfulness theory of relationships shows how closeness in relationships may be enhanced. Minding is the "reciprocal knowing process involving the nonstop, interrelated thoughts, feelings, and behaviors of persons in a relationship." Five components of "minding" include:
- Knowing and being known: seeking to understand the partner
- Making relationship-enhancing attributions for behaviors: giving the benefit of the doubt
- Accepting and respecting: empathy and social skills
- Maintaining reciprocity: active participation in relationship enhancement
- Continuity in minding: persisting in mindfulness
After studying married couples for many years, psychologist John Gottman has proposed the theory of the "magic ratio" for successful marriages. The theory says that for a marriage to be successful, couples must average a ratio of five positive interactions to one negative interaction. As the ratio moves to 1:1, divorce becomes more likely. Interpersonal interactions associated with negative relationships include criticism, contempt, defensiveness, and stonewalling. Over time, therapy aims to turn these interpersonal strategies into more positive ones, which include complaint, appreciation, acceptance of responsibility, and self-soothing. Similarly, partners in interpersonal relationships can incorporate positive components into difficult subjects in order to avoid emotional disconnection.
In addition, Martin Seligman proposes the concept of Active-Constructive Responding, which stresses the importance of practicing conscious attentive listening and feedback skills. In essence, practicing this technique aims to improve the quality of communication between members of the relationship, and in turn the gratitude expressed between said members.
Capitalizing on positive events
People can capitalize on positive events in an interpersonal context to work toward flourishing relationships. People often turn to others to share their good news (termed "capitalization"). Studies show that both the act of telling others about good events and the response of the person with whom the event was shared have personal and interpersonal consequences, including increased positive emotions, subjective well-being, and self-esteem, and relationship benefits including intimacy, commitment, trust, liking, closeness, and stability. Studies show that the act of communicating positive events was associated with increased positive affect and well-being (beyond the impact of the positive event itself). Other studies have found that relationships in which partners responded to "good news" communication enthusiastically were associated with higher relationship well-being.
Neurobiology of interpersonal connections
Humans are social creatures, and there is no other behavioral process that is more important than attachment. Attachment requires sensory and cognitive processing that lead to intricate motor responses. As humans, the end goal of attachment is the motivation to acquire love, which is different from other animals who just seek proximity.  There is an emerging body of research across multiple disciplines investigating the neurological basis of attachment and the prosocial emotions and behaviors that are the prerequisites for healthy adult relationships. The social environment, mediated by attachment, influences the maturation of structures in a child's brain. This might explain how infant attachment affects adult emotional health. Researchers are currently investigating the link between positive caregiver–child relationships and the development of hormone systems, such as the hypothalamic–pituitary–adrenal axis (HPA axis) and Oxytocinergic system. In order to accurately study the neurobiology of interpersonal connection, the behavior must fulfill three requirements. The first is that the behavior must have a noticeable onset so that researchers are able to examine the formation of the attachment bond or how it is inhibited. Second, the behavior must be selective in order differentiate it from normal social interaction. Lastly, the behavior being studied has to be testable so it can be measured and manipulated, in order to establish reliability.
- The mother–infant attachment – Key biological factors have emerged that can explain the motivation behind maternal caregiving behavior in humans and mammals. However, it does differ from species to species, due to that some species only exhibit maternal care postpartum, others exhibit it only slightly and some are very maternal. Two main neuroendocrine systems that revolved around Oxytocin and Dopamine,  and another neuropeptide, prolactin are directly involved as mediators of maternal care. The mother–infant bond is so complex and strong due to these biological systems, that a response to maternal separation exists. The response to separation is due to the withdrawal of several different components from behavioral and biological systems. Separation anxiety, the psychological term that describes when the response that occurs infant is separated from the mother, causes loss of those components, as seen in studies done with rats. 
- Oxytocinergic system – Oxytocin is a peptide hormone produced in the hypothalamus that is passed through the posterior pituitary gland into the bloodstream. Oxytocin acts on the mammary glands and uterine muscles to stimulate the secretion of milk and uterine contractions during childbirth. However, it is a crucial factor in many aspects of social bonding,specifically the onset of the mother–infant attachment bond. It acts on the medial preoptic area (MPOA) and the ventral tegmental area (VTA) in the brain which are critical for integration of sensory information in maternal care.Oxytocin plays a key role in physical proximity and nurturing care and leads (as shown in studies with rats) the mother to go from avoiding behavior to caring for their young. Oxytocin knockout rats or injection of an oxytocin receptor antagonist will lead to neglect of the infant or pup.  In mammals, the development of the Oxytocinergic system has led to the basis of the mother–infant attachment.
- Dopaminergic system – Dopamine is a neurotransmitter that affects behavior in not just the mother but in the offspring as well. Dopamine is essential in for reinforcing behavior that gives us pleasure because it is part of the limbic system that deals with emotion. Therefore, it is able to stimulate responsive maternal care and reinforce attachment. Understanding the dopaminergic system is important because it could make the difference between maternal neglect and nurture. 
- Prolactin – As seen in lesion studies of rats prolactin, which is also involved in lactation, is important in encouraging maternal behavior. Decreasing the levels of prolactin or lack of the receptor of prolactin leads to inhibition of maternal care in rats.
- Adult–adult pair bond formation – Oxytocin and vasopressin play a crucial part in the process of bond formation of mates. Vasopressin is a peptide hormone whose main function is to retain water in the body, and is also known as antidiuretic hormone (ADH). Pair bonding is studied using voles and it has been found that injection of both hormones stimulates the behavioral responses needed in pair bond formation, even when mating hasn't occurred.These results are also proven when injection of receptor antagonists of this hormones inhibits mating and necessary behaviors.
The ability to study the biological processes behind attachment allows scientists to be able to understand the fundamental levels to makeup a psychological construct. It provides a link between a psychological concept and it's physiological foundation. 
Researchers are developing an approach to couples therapy that moves partners from patterns of repeated conflict to patterns of more positive, comfortable exchanges. Goals of therapy include development of social and interpersonal skills. Expressing gratitude and sharing appreciation for a partner is the primary means for creating a positive relationship. Positive marital counseling also emphasizes mindfulness. The further study of "flourishing relationships could shape the future of premarital and marital counseling as well."