On the Meaning of Transubstantial
To me, the prefix "trans" is the key.
- Transformation is change of form
- Transmutation is change of shape
- Transfiguration is change of appearance
- Transubstantiation is the change of substance.
While often one will be related to another, it does not follow that there is a co-dependence. So, while it is possible that something will change forms but not substance or shape (ice will change to water to steam and back and, given the right circumstances, that can all be in the same shape), it is also possible that the substance of a thing can change without a change to the form, shape, or appearance (this is not to discount Eucharistic miracles where both the form and substance of the host changed).
Admittedly, it is difficult to give an example of "change of substance" in nature, because so much of nature is of the same substance. But, there are two things we can use to inform our understanding. First, an example might be found in a piece of paper. A piece of paper, so long as there are no intelligible writings on it, is merely a piece of paper. Once it has intelligible markings, however, it becomes significant. It becomes a letter or a pamphlet or a list. Admittedly, this does have some easily detectable change of form, but the change in significance is far greater than any change in appearance.
The other fact we might use to inform ourselves on the nature of substance is the Creed. Recently, the Catholic Church finally corrected the english translation of the Nicene creed to read, "Consubstantial with the father" (I say finally because for forty odd years it was "one in being", which is a fundamentally incorrect translation of the Latin word, "consubstantialis"). This word implies that we should see the universe as having at least two meta-substances: natural and temporal vs. divine and eternal. It is in this sense that Catholics understand the word, "transubstantial." It is a piece of matter which becomes of the divine substance.
On Justification of the Doctrine
A hint of Scripture
The words of Christ have been debated quite frequently and it is very difficult to say that they must be held as figurative. While I am not willing to enter that debate fully at the moment (that would take quite a bit of time and effort), I will say that it is apparent that communion in the New Testament was something very important (celebrated daily) and that it was very significant (leading to illness if it was mistreated). Both of these strike rather substantial blows against a purely symbolic view of the breaking of the bread.
On the other hand, there is ample evidence from the first 1500 years of the Church that it was the universal belief that the eucharist represented a sacramental reality. This is known in two ways:
- By "sacramental reality" we do not mean, "an outward and visible sign of an inward invisible grace," but rather that a sacrament is, "a symbol which effects itself." Now I know, that word, "symbol" does become a bit vague, but the phrase is understood (in context) to mean, "something which represents something else bringing about and becoming that which it represents." Therefore baptism is not merely the symbol of washing, but it is washing. Marriage is not simply two symbolizing unity, but it is two becoming unified. Eucharist is not merely a symbol of us receiving Christ, but it is actually the divine meal. This belief of the nature of the sacraments is something which is clearly present from the earliest of days.
- Even if that sacramental understanding were missing, there is direct testimony to transubstantiation itself. I know of one eucharistic miracle which predated Constantine. And Ignatius of Antioch (my patron) may not say the word, "transubstantial" directly, but it is harder to say that he did not believe in it than it is to argue that he did (this plus Occam's Razor...).