In a town up by our old lake house, there is a strip mall with a big sign that reads, "Dr. Jeremy Dentum, DDS" (name changed, but prefix and suffix kept intact). Each time I would drive by it, I would get a chuckle thinking that this guy really wants people to know he is a doctor. In fact, there are many people who use the "Dr." in front of their names and "PhD" or other doctoral designation after their names in professional settings. There are also many doctors who simply identify themselves by first name and last name in the same professional settings. However, most seem to use either "Dr." or their designation after their name. I have even heard stories of parents with a doctorate who make their children call them "doctor." So what are the social rules for using the title "doctor"?
To answer this question, I started with a literature review and found nothing. This seems like an area ripe for research. I turned to a very informal survey polling over 100 members of the LinkedIn psychology group, and as expected, the answers varied quite a bit. Here are some of my observations.
No, this is not something that we can just look up in the dictionary. There is a common misunderstanding that dictionaries are prescriptive only, that is, they somehow magically define words. Dictionaries are also descriptive, that is, their entries are derived from common usage. It is a circular process where people are guided by dictionary definitions but not constrained by them, and editors of dictionaries change the definitions based on common usage. Although all dictionaries I checked had some form of the definition that refers to one who as earned the highest educational achievement, this does not answer the question concerning social rules.
Etymology, smetymology. According to several online sources, some form of the word "doctor" originally (circa 1300) meant "religious teacher," "adviser," "scholar," or just "teacher." That is interesting, but certainly does not answer the question about usage in America today. Meanings change over time. Just a century ago, a headline that read "The President is Gay" wouldn't be at all controversial.
Acceptable use is moderated by the academic achievements of the person doing the judging. Those with PhDs tended strongly to support the use of the title "doctor," whereas those without the degree or not working towards it tended to discourage its use outside of the medical profession. Bias is likely to play a role here for both parties.
Confusing "doctor" with "physician." Outside of most professional circles where people earn PhDs and other doctorates besides MDs, the term "doctor" is equated with "physician." Therefore, if one were to be introduced in a casual environment as a doctor, the default assumption would be that the person would be a physician of some kind, therefore be both confusing and misleading. However, if the same introduction took place at a university, there would be little confusion because of the context in which the title was used (i.e., university setting). Descriptively, this is how things appear. However, this does not mean that non medical doctors do not have the right to use the title outside their professional setting, nor does it mean that they shouldn't use the title outside their professional setting. In fact, the more non medical doctors who use their title "doctor," the more the public will understand that the title represents more than just physicians. Increased usage can change this social norm.
The title "doctor" helps define a relationship. By introducing oneself using the title "doctor," there is an unspoken understanding that the person wants to be referred to by "doctor." The exception is when the introduction is followed by, "but you can call me [first name]." By asking (directly or indirectly) that you be referred to by the title "doctor," one is establishing a hierarchical relationship with implied social boundaries that should not be crossed. This would be quite appropriate in a student/professor or client/practitioner relationship, but quite inappropriate if trying to establish a romantic relationship.
It is clear that there are practical advantages that come with the title "doctor" including instant trust, respect, and special treatment. While there is no guarantee that a doctor is any more trustworthy or worthy of respect than any given non doctor, this is a heuristic that is commonly used by many people. However, negative qualities can also be associated with this heuristic such as "pompous," "elitist," and someone who can afford to pay much more than they need to for a product or service. This is where social intelligence comes in—one can assess the situation and choose if using the title would lead to a positive outcome or not.
Two egos. It is clear that a doctor can allow his or her academic achievement to affect the way he or she treats others. What is less clear, is that the egos of the people who judge someone for using the title "doctor" is also part of the equation. For example, a PhD may use the title in what most would consider an appropriate context, but might still be judged harshly by someone who dropped out of graduate school or desperately wanted to get a PhD but never made the commitment. This would be a type of defense mechanism employed to lessen the pain of not attaining a PhD. It would also be understandable that a medical doctor would be more critical of non medical doctors using the title "doctor" in an attempt to have their titles be more exclusive.
Professional advantage. In my book, Year To Success, I wrote a chapter on self-promotion and how too many people are so conscious of being seen as having big egos that their professional lives suffer. I am in no position to tell anyone which values they should live by, but I am in a position to offer advice on which values are not very compatible with financial or professional success—humility is one of them. It is an extremely competitive world, and unless you are the one goat herder in town, it is important for you to be proud of your accomplishments and never sell yourself short. Confidence in oneself is not only a virtue, but a key component in success and well-being. If you have earned a doctorate, your neighbor might not need to know, the other soccer moms don't need to know, and neither does the mailman, but you would be doing yourself a major disservice if you are keeping this achievement a secret in your professional circles.
As for me, when I have officially earned the right to use the title "doctor" or add the letters "PhD" after my name, I will (but never both at the same time). I will also be conscious of the situational and social context, and do my best to remain personally humble while not being afraid to be professionally proud.