To reify is usually defined as mistakenly regarding an abstraction as a thing. It is derived from the Latin word res meaning 'thing'.
Reification in Western philosophy means treating an abstract belief or hypothetical construct as if it were a concrete, physical entity. In other words, it is the error of treating as a "real thing" something which is not a real thing, but merely an idea.
In Buddhist philosophy the concept of reification goes further. Reification means treating any functioning phenomenon as if it were a real, permanent 'thing', rather than an impermanent process.
Now of course we reify all the time. We regard a car as a 'thing', though if we think carefully we realise that it is actually a process. A car is the ultimate example of the impermanence of functioning phenomena. Parts are always needing replacement. The body gradually oxidises to rust and the engine relentlessly becomes ever more worn. In the long term, a car can be regarded as a process that has money as its input and scrap metal as its output.
If we check carefully we realise that ALL functioning phenomena are impermanent, and therefore are processes lacking any inherent identity, rather than fixed 'things' which have some defining essence.
In fact, they could not be functioning phenomena unless they were capable of interchanging their parts or properties with other entities. A car can only function by taking fuel and oxygen in, and putting carbon dioxide and steam out, while absorbing, transmitting and delivering the energy so produced to the wheels. While it is functioning, all the mechanical parts are in a state of impermanence, continually changing their relative positions.
The ultimate truth of all functioning phenomena is that if viewed over a long enough timescale, they are seen to have the ultimate nature of processes. They are impermanent and lack any defining essence that has the power to 'keep them as they are'.
Although it may be true that all functioning things are processes, it doesn't help us to find our way around the everyday world. Conventionally, we regard any object that exists relatively unchanged for a long enough duration to be useful, as a 'thing' rather than a process.
This is similar to the situation where knowing that matter is 99.9% empty space is of no use whatsoever when we're building a brick wall.
So reification of functioning phenomena is a conventional truth - a working approximation that allows us to function in, and find our way around the world.
In Buddhist ontology process is primary, substance is secondary.
"Change and decay in all around I see"
Swift to its close ebbs out life’s little day
Earth’s joys grow dim, its glories pass away
But the entire world that we function in and find our way around is itself a process, and will eventually cease to exist. The world and all that's in it lack any enduring identity that has the power to prevent impermanence from sweeping them all away. That is their ultimate truth.
Even the fundamental particles of matter can never be known as 'things in themselves', they can only be known by their interactions. And those interactions, by their very nature, cause a change of state of what is interacting. So it's impermanence all the way up, and impermanence all the way down.
Existence as a conventional truth
Even the concept of 'existence' is itself a conventional truth. To say that any functioning phenomenon 'exists' is a commonsense approximation to saying that it endures for a relatively long time. 'Existence' is really nothing other than a less blatant form of impermanence.
The validity of the two truths
So both conventional truth and ultimate truth are valid for their respective purposes, in the same way that classical and quantum physics are both valid.
If we want to design and build a bridge, we think in terms of classical physics. If we want to explore the ultimate nature of matter, we think in terms of quantum physics.
Likewise, if we want to build a Dharma center, then we use conventional truths to assemble all the conventionally existing things that are needed - stones, bricks, beams, windows, doors, cables, pipes etc.
If we then want to sit inside the finished Dharma-center and contemplate ultimate truth, we may reflect on how the ultimate truth of the Dharma-center is that it exists dependently upon the causes and conditions that built it, the parts from which it was built, and our mental labelling of it as 'Dharma-center'.
The more you look for it, the less you find it.
If we think that the Dharma-center actually exists from its own side, then we may try to pinpoint the exact stage of its construction at which 'heap of bricks' suddenly ceased to exist and the 'essence of Dharma-center' jumped into the structure to make it the thing that it is.
And of course we'll never find that sudden transformation, because 'essence of Dharma-center' only exists in our own mind, not within the structure of the Dharma-center.
- Sean Robsville
Buddhism and Process Philosophy
Essentialism, Ideal Forms, Plato, Buddhism and Generic Images
Existence, Impermanence and Emptiness in Buddhism
Inherent Existence in Buddhist Philosophy
Sunyata - the emptiness of all things