Though the "Dark Night of the Soul" is a term widely employed in many different circumstances, it is originally associated with the Spanish poet and writer, St. John of the Cross in a specialised spiritual contemplative context.
In common parlance it is now used to refer to a period of special difficulty in one's life.
For example in my own country, many people would have therefore experienced a "dark night of the soul" in terms of dealing with severe aftermath of the recession here following the international financial crisis of 2008.
However in the mystical literature it is used more narrowly to deal with an especially difficult transformation that an advancing contemplative must face before attaining stable union with God.
However, even here the term can be somewhat vague, as several "nights" may be required along this journey.
Indeed St. John refers to a whole series of such "nights". For example he refers to initial "active nights" of both sense and of spirit. Then he deals at greater length with the more severe "passive nights" again of sense and spirit. And in one place he mentions a further "night of will".
Then in her highly influential book, "Mysticism", Evelyn Underhill uses the term "dark night of the soul" to refer to what St. John would identify merely as the "passive night of spirit".
However Underhill makes a valuable distinction here in that for some people (using the Dominican monk, Henry Suso to illustrate) that the active element could be much more pronounced even during its most severe manifestations.
This in turn raises the important point that just as there are a number of distinct personality types (that can for example be identified in terms of the Enneagram or Myers-Briggs classifications) equally the "dark night" would be likely to operate in a distinctive manner for each of these types.
So in fact the account that St. John gives of the process - which is heavily based on his own unique journey - reflects closely a particular personality type.
I remember at one stage becoming keenly interested in this issue when I was attempting to understand why for many years I resonated so strongly with the various details of his experience.
What I concluded was that though the depth endured may indeed have differed, that we both shared very similar personality profiles. Thus in Enneagram terms I would classify St. John as a 4 with a strong 5 wing; in my own case it would be somewhat complementary as a 5 with a strong 4 wing.
There are also good reasons to believe that - in appropriate circumstances - this personality profile would lead to the most extreme manifestations of the "dark night".
When one looks at the diagram representing the Enneagram the only gap (without inter-crossing connections between other numbers) occurs between 4 and 5. This would suggest therefore that the consequent attempt to attain full personality integration (for a personality comprising both 4 and 5) would require the greatest journey in pure faith.
So what always impressed me about St. John's account is that even though it is based to the most intense degree on inner subjective experience (representing the 4 type) he still has the necessary detachment to be able to look at this experience in a systematic objective manner (representing the 5).
However I would like to make the point that substantial personality transformation - even to the extreme lengths of a St. John - is not the preserve of an any one religious tradition. Indeed it can still be entirely valid without being allied to any religious tradition.
So in the Christian tradition the "dark night" will always be identified as arising from the desire for union with God (and indeed a God that is understood very much in terms of its own accepted symbols).
However properly understood the "dark night" will also be part of the experience of anyone who ardently seeks the full integration of personality (which may not be directly interpreted in a religious manner).
Now St. John's account clearly reflects the spirituality of a Roman Catholic monastic order (The Carmelites) at a particular point in Spanish history where open expression was still heavily censored.
One for example may question the validity of an account where the important issue of psychosexual development is completely ignored! Unfortunately honest discussion on this matter has always been taboo in Christian writing (which to my mind represents a huge limitation therefore in its overall value).
So his own writing inevitably suffers from this and is thereby not suited as a universal template for all such experiences.
Also it suffers from the problem I was mentioning - which perhaps St. John did not properly appreciate - that his account reflects the experience of just one personality type. Did he seriously consider in writing up his account that it could be applied unmodified to all spiritual proficients (even within his own order)?
Perhaps my greatest reservation with this whole approach is that it is so exclusively tied up with spiritual transformation. Therefore, the important changes in intellectual and affective experience, that accompany each stage of spiritual growth, are almost entirely ignored. This is a very important point! For if appropriate affective and cognitive structures are not properly developed at each stage, this in itself will set severe limitations to further spiritual transformation (of a balanced nature) .
For example we may validly ask - though apparently not many do - what is the implication of a dramatic "dark night" episode for example with respect to one's understanding of physics or mathematics?
Or from the affective point of view what is the effect of such an experience on the nature of psycho sexual development?
Thus in an attempt to get away from this exclusive religious identification of the "dark night", I have tended recently to use more Jungian based language. This hopefully can incorporate the benefits of the traditional approach, while opening up the experience as an integrated stage of advancing psychological development.
Thus the "dark night" always relates to a special intensification with respect to holistic unconscious development.
Also it does not inevitably pass, so that one is soon back again in the world of conscious symbols.
When development is especially deep, one may spend most of one's remaining existence in the darkness of the unconscious (thus remaining in the "dark night") though as in a cinema periodically become better accustomed to "seeing" in this darkness. Such an experience would be consistent with an unbroken awareness of spirit as ever present in reality, but yet in a way that is rarely filled with any consoling light (as consciously manifested).
This is now becoming apparent from the accounts of well known saints such as Paul of the Cross and Mother Teresa of Calcutta.
But again such experiences should not be exclusively identified with recognised saints of this tradition, as it greatly limits appreciation of the many roads that can be taken to reach the same destination.