Trying to rationalise and articulate wabi-sabi appears largely been avoided because it is fundamentally dealing in terms of emotional experience and the essence of things. By trying to explain Wabi-Sabi in writing almost goes against the very idea of wabi-sabi; If all things are incomplete, how can they be fully documented and, likewise, if all things are imperfect?; if all things are impermanent, how will the documentation unfold over time? Obscurantism is a defining feature of wabi-sabi and it almost relies on mystery to uphold its elusive 'specialness'. Western authors of wabi-sabi often state that the concept seems intentionally avoided in Japanese discourse because of its obfuscation: 'the concept is so full of thorny issues for the Japanese intellectual' (Koren, 1994:10). As an emotive concept, of course, it is inarticulable. I do not speak Japanese but from everything I understand, the conventions of the language is better at conveying subtleties in emotion and less so at rationalising by comparison to the western dialect. There is a direct correlation to art and photography here in so far as essences are approximated as opposed to facts truthfully told.

There are however standard definitions that scratch the surface. We can say that wabi-sabi is a traditional Japanese cultural aesthetic born from a world view centred on the acceptance of transience and imperfection. Wabi-Sabi is peripherally associated with Zen Buddhism as a derivative from the Buddhist teaching of the three marks of existence (三法印, sanbōin), most notably 'impermanence' (無常, mujō), 'suffering' (苦, ku) and 'emptiness' or 'absence of self-nature (空, ). It is an aesthetic that speaks of accepting and appreciating the "imperfect, impermanent, and incomplete" flows of existence found in nature. "Wabi-Sabi is an intuitive appreciation of transient beauty in the physical world that reflects the irreversible flow of life in the spiritual world. It is an understated beauty that exists in the modest, rustic, imperfect, or even decayed, an aesthetic sensibility that finds a melancholic beauty in the impermanence of all things." (Juniper, 2003:51)

Impermanence (無常, mujō): All things are impermanent and are heading towards 'nothingness', be that tangible (rocks, planets and stars) or intangible (reputation, heritage, memory, cultures, theory, language), analogue or digital form, will eventually fade into nonexistence. Does a photograph make something permanent? Does a negative deteriorate or even a platinum print eventually fade? What of a digital file saved in a format that will inevitably become obsolete and unreadable? Does the image cease to exist in the making of a copy to a new format?

Imperfection: Nothing in existence is perfect, or rather, nothing exists without imperfection. Even the most seemingly perfect straight edge will have flaws when magnified. Over time, everything becomes more irregular and flawed. Is there a perfect photograph? In whose eyes is it perfect?

Incompleteness: All things in our universe, including the universe itself, are in an undeniable state of deterioration, nothing is ever finished not complete. At what point is a wave or a tree complete? Is a photograph finished when it is taken? or does it take on new meaning as soon as it is taken and distributed to myriad different subjective audiences?

In Wabi-Sabi for Artists, Designers, Poets & Philosophers (1994), Leonard Koren attempts to lay out Wabi-Sabi as a referential 'comprehensive aesthetic system'. The table below is a breakdown of the key interrelating aspects:

Metaphysics:All things are either evolving from, or devolving towards, 'nothingness'. While the universe constructs, it also destruct. New things emerge out of 'nothingness', which, opposed to the traditional western thought that nothingness is an empty space, in Wabi-Sabi it is a place alive with possibility. The universe is in constant motion towards or away from potential.
(p42)
Spiritually Values:Truth comes from the observation of nature, 'greatness' exists in the inconspicuous and overlooked details, beauty can be coaxed out of ugliness.
(p47)
State of Mind:Acceptance of the inevitable. Wabi-Sabi is an aesthetic appreciation of the evanescence of life. Appreciation of the cosmic order - Wabi-Sabi suggests the subtlest realms and all the mechanics and dynamics of existence, beyond what our ordinary sense can perceive. Primordial forces are evoked in a similar way that medieval cathedrals were constructed to emotionally convey their respective cosmic themes.
(p55-57)
Moral Precepts:Do away with all that is unnecessary, stop preoccupation with success, wealth, power and luxury. focus on the intrinsic and ignore material hierarchy.
'Material Poverty' / 'Spiritual Richness'.
(p59-61)
Material Qualities:The suggestion of the natural process, irregular, intimate, unpretentious, earthy, murky, simple. The materials that things Wabi-Sabi are made elicit transcendent emotions to represent deep underlying physical forces and structure of everyday life.
(p62-72)
The Wabi-Sabi Universe, Koren (1994:40-41).

There is no direct translation of "wabi" and "sabi"; and their original meanings have evolved over time like all cultures and languages. The original meaning of the word Wabi related to the loneliness of living in nature, remote from society: "Wabi originally meant the misery of living alone in nature, away from society, and suggested a discouraged, dispirited, cheerless emotional state. The self-imposed isolation and voluntary poverty of the hermit and ascetic came to be considered opportunities for spiritual richness. For the poetically inclined, this kind of life fostered an appreciation of minor details of everyday life and insights into the beauty of the inconspicuous and overlooked aspects of nature. In turn, unprepossessing simplicity took on new meaning as the basis of a new pure beauty" (Koren, 1994:22). Over time, Wabi has come to refer more to the simple, understated and quiet (and the uniqueness of the minute flaws and anomalies that come in the process of production) found in both natural and man-made objects. 'Sabi' originally meant "chill", "lean" or "withered" and over time has come to refer to the serene beauty found in the 'timeworn' - the history of an object, or person, visible in its timeworn surfaces (faded, cracked, repaired patinas, the wrinkled skin warts and all). The two words together ‘wabi-sabi’ come to mean embracing and aesthetic appreciation of ageing, flaws, and the beauty of the undeniable effects of time and imperfections.

Wabi (refers to)Sabi (refers to)
A way of life, a spiritual pathMaterial objects
The inward, the subjectiveThe outward, the objective
A philosophical constructAn aesthetic ideal
Spatial EventsTemporal Events
The Wabi and Sabi Charateristics, Koren (1994:23).

References:
Koren, Leonard (1994) Wabi-Sabi for Artists, Designers, Poets & Philosophers. California: Imperfect Publishing.
Juniper, Andrew (2003) Wabi Sabi: The Japanese Art of Japanese of Impermanence. Tuttle Publishing