Imaginary friends or imaginary companions are a psychological and social phenomenon where a friendship or other interpersonal relationship takes place in the imagination rather than external physical reality. Although they may seem very real to their creators, children usually understand that their imaginary friends are not real. The first studies focusing on imaginary friends are believed to have been conducted during the 1890s. There is very little information about the development and the appearance of imaginary friends in children. However, Klausen & Passman (2007) report that imaginary companions were originally described as being supernatural creatures and spirits that were thought to connect people with their past lives. Adults in early historic times had entities of household gods, guardian angels, and muses that served to function as an imaginary companion to provide comfort, guidance, and inspiration for creative work. Eventually, the phenomenon of imaginary companions had passed on to children. The appearance of imaginary friends in the lives of children is unknown, but it is possible that the phenomenon appeared in the mid – 20th century when childhood was emphasized to be an important time for children to play and to use their imagination.
Imaginary friends are made often in childhood, sometimes in adolescence, and rarely in adulthood. They are people or other characters created in the mind that the creator interacts with. In some studies, imaginary companions are defined as children impersonating a specific character (imagined by them), or objects or toys that are personified.  However, some psychologists will define an imaginary friend only as a separate created character. Imaginary friends or imaginary companions can be people, but they can also take the shape of other characters, such as animals, or other abstract ideas such as ghosts, monsters, angels, etc.  These characters can be created at any point during a lifetime, though Western culture suggests they are most acceptable in preschool and school age children.  They often function as tutelaries when played with by a child. They reveal, according to several theories of psychology, a child's anxieties, fears, goals and perceptions of the world through that child's conversations. They are, according to some children, physically indistinguishable from real people, while others say they see their imaginary friends only in their heads, and still others cannot see the friend at all but can sense his/her presence. In regards to having imaginary friends, most of the prior research agrees that girls are more likely to develop imaginary friends than boys. Past research agrees that boys are more likely to participate in fantasy play, and they incorporate the themes of superheroes and adventure in their fantasy play while girls mostly play dress-up and play house. Once children reach school age, boys and girls are equally likely to have an imaginary companion.  And research has often reiterated that there is not a specific "type" of child that creates an imaginary friend. 
Research has shown that imaginary companions are a normative part of childhood, and even adulthood.  And some psychologists  suggest that imaginary companions are much like a fictional character created by an author. As Eileen Kennedy-Moore points out, "Adult fiction writers often talk about their characters taking on a life of their own, which may be an analogous process to children’s invisible friends." In addition, Marjorie Taylor and colleagues have found that fiction writers are more likely than average to have had imaginary companions as children.
There is a difference between the common imaginary companion that many children create, and the imaginary companions of psychopathology. Often when there is a psychological disorder, and an imaginary companion is present, the creator believes that this companion is real, and does not differentiate between the real and imagined. 
Imaginary friends or companions can serve many different functions. Playing with ICs enables children to enact behaviors and events that they have not yet experienced. Imaginary play allows children to use their imagination to construct knowledge of the world. In addition, ICs might also fulfill children’s innate desire to connect with others before actual play among peers is common. According to psychologist Lev Vygotsky, cultural tools and interaction with people mediate psychological functioning and cognitive development. Imaginary companions, perceived as real beings, could teach children how to interact with others along with many other social skills. Vygotsky’s sociocultural view of child development includes the notion of children’s “zone of proximal development,” which is the difference between what children can do with and without help. Imaginary companions can aid children in learning things about the world that they could not learn without help, such as appropriate social behavior, and thus can act as a scaffold for children to achieve slightly above their social capability.
In addition, imaginary companions also serve as a means for children to experiment with and explore the world. In this sense, ICs also relate to Piaget’s theory of child development because they are completely constructed by the child. According to Piaget, children are scientific problem solvers who self-construct experiences and build internal mental structures based on experimentation. The creation of and interaction with ICs helps children to build such mental structures. The relationship between a child and his or her IC can serve as a catalyst for the formation of real relationships in later development and thus provides a head start to practicing real-life interaction.
It has been theorized that children with imaginary companions may develop language skills and retain knowledge faster than children without them, which may be because these children get more linguistic practice than their peers as a result of carrying out "conversations" with their imaginary friends.
Kutner (n.d.) reported that 65% of seven-year old children report they have had an imaginary companion at some point in their lives. He further reported:
Imaginary companions are an integral part of many children's lives. They provide comfort in times of stress, companionship when they're lonely, someone to boss around when they feel powerless, and someone to blame for the broken lamp in the living room. Most important, an imaginary companion is a tool young children use to help them make sense of the adult world.
Taylor, Carlson & Gerow (c2001: p. 190) hold that:
despite some results suggesting that children with imaginary companions might be superior in intelligence, it is not true that all intelligent children create them.
If imaginary friends can provide assistance to children in developing their social skills, they must function as important roles in the lives of children. Hoff (2004 – 2005) was interested in finding out the roles and functions of imaginary friends and how they impacted the lives of children.  The results of her study have provided some significant insight on the roles of imaginary friends. Many of the children reported their imaginary friends as being sources of comfort in times of boredom and loneliness. Another interesting result was that imaginary friends served to be mentors for children in their academics. They were encouraging, provided motivation, and increased the self – esteem of children when they did well in school.  Finally, imaginary friends were reported as being moral guides for children.  Many of the children reported that their imaginary friends served as a conscious and helped them to make the correct decision in times where morality was questioned. 
Some psychologists[who?] have suggested that older children may retain but stop speaking about imaginary friends due to adult expectations and peer pressure. Pediatrician Benjamin Spock believed that imaginary friends past age four indicated that something was "lacking" in the child or his environment. Some have theorized that children who hold on to imaginary friends past school-age are stigmatized.
Other professionals feel that imaginary friends are common among school-age children and are part of normal social-cognitive development.Part of the reason that people believed that children gave up imaginary companions earlier than they do, is related to Piaget's stages of cognitive development. Piaget suggested that imaginary companions disappeared once children entered the concrete operational stage of development.  Marjorie Taylor identified middle school children with imaginary friends and followed up six years later as they were completing high school. At follow-up, those who had imaginary friends in middle school displayed better coping strategies but a "low social preference for peers." She suggested that imaginary friends may directly benefit children's resiliency and positive adjustment. Because imagination play with a character involves the child often imagining how another person (or character) would act, research has been done to determine if having an imaginary companion has a positive effect on theory of mind development.  In a previous study, Taylor & Carlson (1997) found that 4 year – old children who had imaginary friends scored higher on emotional understanding measures and that having a theory of mind would predict higher emotional understanding later on in life.  When children develop the realization that other people have different thoughts and beliefs other than their own, they are able to grow in their development of theory of mind as they begin to have better understandings of emotions. 
Positive Psychology and Imaginary Companions
The article, “Pretend play and positive psychology: Natural companions” defined many great tools that are seen in children who engage pretend play. These five areas include creativity, coping, emotion regulation, empathy/emotional understanding and hope (Pearson, Russ & Spannagel, 2008). Hope seems to be the underlying tool children use in motivation (Pearson, Russ & Spannagel, 2008). Children become more motivated when they believe in themselves, therefore children will not be discouraged to come up with different ways of thinking because they will have confidence (Pearson, Russ & Spannagel, 2008). Imaginary companionship displays immense creativity helping them to develop their social skills and creativity is frequently discussed term amongst positive psychology (Pearson, Russ & Spannagel, 2008). An imaginary companion can be considered the product of creativity whereas the communication between the imaginary friend and the child is the process (Pearson, Russ & Spannagel, 2008).
Research in the area of adolescence and Imaginary companions
“Imaginary Companions in adolescence: sign of a deficit or positive development?” explores the extent to which adolescents create imaginary companions (Siffge-Krenke, 1997). The researchers explored the prevalence of imaginary companions in adolescence by investigating the diaries of adolescents age 12-17 (Siffge-Krenke, 1997). In addition they looked at the characteristics of these imaginary companions and did a content analysis of the data obtained in the diaries (Siffge-Krenke, 1997). There were three hypotheses tested: (1) the deficit hypothesis, (2) the giftedness hypothesis, (3) the egocentrism hypothesis (Siffge-Krenke, 1997). The results of their study concluded that creative and socially competent adolescents with great coping skills were particularly prone to the creation of these imaginary friends (Siffge-Krenke, 1997). These findings did not support the deficit hypothesis or egocentrism hypothesis, further suggesting that these imaginary companions were not created with the aim to replace or substitute a real life family member or friend, but they simply created another “very special friend” (Siffge-Krenke, 1997). This is surprising because it is usually assumed that children who create imaginary companions have deficits of some sort, and in addition for an adolescent to have an imaginary companion is unheard of (Siffge-Krenke, 1997). Despite the many stigmas of imaginary companions this research shows that imaginary companions are not only created by adolescents but these adolescents are well developed and do not have deficits. This research severs as great evidence in this great debate of imaginary companions being a source of positive development. In addition this shows that imaginary friends can actually be more of a benefit rather than a harmful creation. Also, this research is in particular unique because it looked at adolescents rather than children, which is not common of imaginary companion studies.
Research in the area of Birth Order and Imaginary Companions
To uncover the origin of imaginary companions and learn more about the children whom create it is necessary to seek out children who have created imaginary companions (Gleason, Sebanc & Hartup, 2000). Unfortunately young children cannot accurately self-report, therefore the most effective way to gather information about children and their imaginary companions is by interviewing the people who spend the most time with them. Often mothers are the primary caretakers who spend the most time with a child. Therefore for this study 78 mothers were interviewed and asked whether their child had an imaginary friend (Gleason, Sebanc & Hartup, 2000). If the mother revealed that their child did not have an imaginary companion than the researcher asked about the child’s tendency to personify objects (Gleason, Sebanc & Hartup, 2000). In order to convey the meaning of personified objects the researchers explained to the mothers that it is common for children to choose a specific toy or object that they are –particularly attached too or fond of (Gleason, Sebanc & Hartup, 2000). For the object to qualify as a personified object the child had to treat it as animate (Gleason, Sebanc & Hartup, 2000). Furthermore, it is necessary to reveal what children consider an imaginary friend or pretend play. In order to distinguish a child having or not having an imaginary companion, the friend had to be in existence for at least one month. In order to examine the developmental significance of preschool children and their imaginary companions the mothers of children were interviewed (Gleason, Sebanc & Hartup, 2000). The major conclusion from the study was the there is a significant distinction between invisible companions and personified objects (Gleason, Sebanc & Hartup, 2000). A significant finding in this study was the role of the child’s birth order in the family in terms of having an imaginary companion or not. The results of the interviews with mothers indicated that children with imaginary friends were more likely to be a first-born child when compared to children who did not have an imaginary companion at all (Gleason, Sebanc & Hartup, 2000). This study further supports that children may create imaginary friends to work on social development. The findings that a first-born child is more likely to have an imaginary friends sheds some light on the idea that the child needs to socialize therefore they create the imaginary friend to develop their social skills. This is an extremely creative way for children to develop their social skills and creativity is frequently discussed term amongst positive psychology (Pearson, Russ & Spannagel, 2008). An imaginary companion can be considered the product of creativity whereas the communication between the imaginary friend and the child is the process (Pearson, Russ & Spannagel, 2008).
In regards to birth order there is also research on children who do not have any siblings at all. The research in this area further investigates the notion that children create imaginary companions due to the absence of peer relationships (Gleason, 2004). A study that examined the differences in self-talk frequency as a function of age, only-child, and imaginary childhood companion status provides a lot of insight to the commonalties of children with imaginary companions (Brinthaupt & Dove, 2012). The researchers collected information from college students who were asked if they ever had an imaginary friend as a child (Brinthaupt & Dove, 2012). There were three studies within the one study and they found that there were significant differences in self-talk between different age groupings (Brinthaupt & Dove, 2012). Their first study indicated that only children who create imaginary companions actually engage in high levels of positive self-talk had more positive social development (Brinthaupt & Dove, 2012). They also found a gender difference within their study that women were more likely than men to have an imaginary companion (Brinthaupt & Dove, 2012). Their findings were consistent with other research supporting that it is more common for females to have imaginary companions (Brinthaupt & Dove, 2012). One possible explanation the researchers suggested that women may be more likely to have imaginary companions is because they are more likely to rely on feedback from other than themselves supporting the conclusions that men were found to have more self reinforcing self-talk (Brinthaupt & Dove, 2012). Furthermore, other research has concluded that women seek more social support than men, which could be another possibility for creating these imaginary companions. (Brinthaupt & Dove, 2012). The second study found that children without siblings reported more self-talk than children with siblings and the third study found that the students who reported having an imaginary friend also reported more self talk than the other students who did not have imaginary friends (Brinthaupt & Dove, 2012). Self-talk is often associated with negative effects such as increased anxiety and depression when the self-talk is specifically negative (Brinthaupt & Dove, 2012). The researchers found that “Individuals with higher levels of social-assessment and critical self-talk reported lower self-esteem and more frequent automatic negative self-statements” (Brinthaupt & Dove, 2012). However, there is also a positive side to positive self-talk and in this study they found that, “people with higher levels of self-reinforcing self-talk reported more positive self-esteem and more frequent automatic positive self-statements” (Brinthaupt & Dove, 2012). They also found that men had a more frequent self-reinforcing self-talk than females (Brinthaupt & Dove, 2012). This particular finding is important because there are not many general findings comparing men and women in adult self-talk in today’s research. Self-talk and imaginary companionship contain many similarities therefore it is possible that they can be related. Through positive self-talk children can increase their self-esteem, which leads to the possibly that a positive relationship with an imaginary companion could predict a similar outcome.
- Wilson, imaginary friend of Chuck Nolland in Cast Away.
- Tony, imaginary friend of Danny in The Shining.
- Charles Herman, imaginary friend of John Nash in A Beautiful Mind.
- Captain Howdy, imaginary friend of Regan McNeil in The Exorcist
- Ivan, imaginary friend of Trevor Reznik in The Machinist.
- Fred, imaginary friend of Elizabeth Cronin in Drop Dead Fred.
- Tyler Durden, imaginary friend of the unnamed narrator in Fight Club.
- Harvey, imaginary friend of Elwood P. Dowd in Harvey.
- Larry Houdini, imaginary friend of Darwin, and Zoe, imaginary friend of Frances in Don't Look Under the Bed.
- Marc Imran and Elle Maya, imaginary friends of Hareez in Real Life.
- Frank, imaginary friend of Donnie Darko.
In other media
- Bloo, imaginary friend of Mac, and many of the characters from Foster's Home for Imaginary Friends.
- Plank, imaginary friend of Jonny 2x4 in Ed, Edd n Eddy.
- Gretchen, imaginary friend of Elizabeth (Stephanie Berrington) in Father Goose: His Book.
- Nadine, imaginary friend of D.W. in Arthur.
- Millie the Mermaid, imaginary friend of Zuri in Jessie.
- Sean Murphy, imaginary friend of Martin Moone in Moone Boy
- Soren Lorensen, imaginary friend of Lola in Charlie and Lola.
- Squirrly (a deceased pet squirrel), Jeffy (a garden hose), Vanessa (an apple), Dewey (a paper towel roll), and Boxy Brown (a cardboard box) are imaginary friends of Meatwad in Aqua Teen Hunger Force.
- In The 7D episode "Buckets," the ghost girl Buckets (played by Kate Micucci) turns out to be the imaginary friend of Queen Delightful (who was nicknamed "Mopsy" by Buckets).
- Taylor, M. (1999) Imaginary Companions and the Children Who Create Them. New York: Oxford University Press.
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- Imaginary Friends with Dr Evan Kidd podcast interview with Dr Evan Kidd of La Trobe University