Click on almost any standard health site, such as Web-MD, and look up “depression” and it will report that depression is different than normal sadness. The site will normally proceed to proclaim that, unlike normal sadness, depression is a "treatable medical condition". Unfortunately, differentiating depression from sadness by describing the former as “a treatable medical condition” does not really explain what depression is; it only tells you that you need to see a doctor.
So, let’s be very clear about what depression is and then proceed to see why we can characterize depressive episodes in terms of depressive reactions, depressive disorders, and depressive diseases.
To start, let’s follow the lead of Web-MD and other medical sites by acknowledging that it is absolutely the case that, although they are related, sadness and depression are very different entities. Let me give a personal example. When I was in graduate school, I foolishly left the back door of our apartment open before heading off to work the lunch shift at a local restaurant. When I returned home, I found one of my dogs, Priscilla, sitting strangely alone in the middle of the living room, anxiously looking up at me and not moving. I recall noting how odd she looked and how weird it was that my other dog, Spencer, was not with her. I quickly saw that the back door was open and immediately feared the worse. Ten minutes later, my worst fears were realized, as I found Spencer lying motionless on the side of the road.
I was crestfallen and recall weeping profoundly in the hours following that discovery. But although I was deeply sad (and, yes, even wracked with guilt) in the days that followed, I was not depressed nor did I become depressed.
So what is the difference between sadness and depression? Sadness is an emotional reaction to loss. It is your motivational-emotional system’s way of signaling that something you valued or something you hoped would come true was lost. Sadness is the way we digest the pain of our loss. Guilt is the signal that you failed to do something you ought to have done and, in failing to do so, someone got hurt. You can see why I felt both sad and guilty in the above example.
Depression, in contrast to sadness, is a state of mental behavioral shutdown. It occurs when the whole system of psychological investment is “dead ended”, meaning the system cannot track or identify any positive or productive pathways of investment (or ways of being). We can look at the key symptoms of depression and see that they are part of a syndrome of behavioral shutdown.
The most prominent symptom is a general increase in negative emotion, especially feelings of futility, despair, powerlessness, and hopelessness. Also jacked up are feelings of fear and anxiety (future threat), shame, guilt and vulnerability, and frustration, bitterness and irritability.
The second most prominent symptom of depression—indeed the most important diagnostic symptom—is “anhedonia”, which is the technical term of loss of pleasure and interest. In other words, whereas the negative affect system is jacked up, the positive affect system is toned down or muted. Desire, interest, excitement, joy, are all lessened or deadened.
So why, according to the shutdown model, are your negative emotion systems jacked up and your positive emotion systems muted? Because when you are depressed a fundamental shift has happened in your motivational-emotional investment system. Basically, a subconscious calculation has taken place that says what you are doing is not working, that you have tried the best you can and there are no good solutions, and so your system is shutting down the positive investment system and gets defensive by activating the negative/avoidance system to try to avoid further failed investments.
Virtually all the other symptoms of depression, including fatigue/lack of energy, difficulty with attention and concentration, disruptions in sleeping and eating, thoughts of death or escape, are consequences that stem from the fundamental motivational-emotional shutdown.
So instead of describing depression as "not normal sadness but a treatable medical condition”, we should instead should be clear that depression is a state of mental/behavioral shutdown (see here for more detail about this).
With this frame, we can down shift gears and think about depression from a new angle. We can ask: What causes mental behavioral shutdowns? With this question, we can then begin to separate the causes from the symptoms and develop a logical classification of at least three conceptually different “kinds” of depressions, what I refer to as depressive reactions, depressive disorders, and depressive diseases.
1. Depressive reactions are when the mental-behavioral shutdown makes perfect sense, given the context. If, for example, it had been my child instead of my dog who had died, and it is quite possible that I simply could never forgive myself for that mistake, it is very possible that I would have become depressed over time. Being depressed following the death of a child or in other contexts that do not allow one to get their basic psychosocial needs met (e.g., being chronically abused or mistreated, being locked up, being completely isolated and alone, feeling unloved and unwanted, and so forth) is perfectly understandable based on the model. (Note, it is because folks recognize the connection between depression and profound grief that there has historically been a bereavement clause in diagnosing depression—it is an acknowledgement of the concept of depressive reactions).
2. Depressive disorders is the term we should use when the depressive reactions turn out to cause additional problems with adjustment and this in turn creates a vicious, maladaptive cycle. This is something I see all the time working with college students. Folks come to college hoping for a wonderful experience, and then they get to college and find they don’t fit in and struggle with the academics. This makes them anxious, which in turn makes them less socially confident and less effective in concentrating, planning, and getting their work done. This causes more trouble and in a couple of weeks their emotional system gets exhausted and starts to “shutdown”. This psychological shutdown in the college setting produces even more dysfunction, and the cycle is completed. But, it is worth noting that, conceptually, there is no need to posit any sort of biological malfunction here.
3. Depressive diseases is the category to describe when the mental behavioral shutdown is far greater than can possibly be explained by basic psychological adjustment problems and when the symptoms are very resistant to changing even when the psychological and social systems are available to support that change. Like many who study depression, I believe we should call depressive diseases melancholic depression and they should be differentiated from “neurotic” depressive disorders.
Defining depression as “a treatable medical condition” is not meaningful because it doesn’t say anything about what depression is. Rather it points to the hyper-medicalization of psychological processes. That said, it is absolutely the case that being depressed says a lot about one’s psychological health and functioning. It means one is NOT flourishing, and is dealing with serious motivational-emotional issues at some level that require attention.
The action that is required, however, should depend on how folks make sense out of the symptoms, namely whether the current depressive episode is an understandable reaction to the environment, a maladaptive psychological cycle, or a pervasive, oppressive, unresponsive mood state that warrants the label “disease”.