This is a word that was invented by Catholics during the Council of Trent in the late 1600’s, but was by no means an innovation to Catholic theology. It’s a concept that Christians up to a certain date have believed since the beginning, but only felt the need to articulate and find a word for during the continental Reformation. Much like all rules, there’s no need to define them until someone breaks them. The only reason there are signs posted around hotel pools saying “NO HORSING AROUND” is because someone, somewhere, horsed around a hotel pool. At that point, a rule which may have seemed arbitrary to a casual hotel attendee was enshrined in hotel law.
“Transubstantiation” may be among the most intimidating of terms when it comes to Catholic vocabulary. However, all it means is that the substance of the bread and wine become “transformed” into the body and blood of Christ. It doesn’t mean that the physical appearance changes. Aristotle laid down the best terms for this discussion- he put forth the notion that there was a difference between substance and accidents. Substance is what a thing actually is, while accidents point to what a thing appears to be. Therefore, when Catholics talk about Christ’s body and blood being present in the Eucharist, they mean he’s actually there, even if he isn’t visibly there. And that you're not likely to consume him and think to yourself, “hmmm… tastes like Jesus.”
There are those, like Bill Maher, who argue that “You can’t be a rational person six days of the week and put on a suit and make rational decisions and go to work and, on one day of the week, go to a building and think you’re drinking the blood of a 2,000-year-old space god.” Atheists and fundamentalists have this in common, as evidenced by the fact that John Knox published a whole treatise based on the premise that he “affirmed the Mass to be, and at all times to have been, idolatry.”
So are Catholics cannibals? Or idolaters? Or are people that invented the doctrine of the transubstantiation as a trump card against the continental Reformation unconcerned about the needs of the average person who prefers smaller words? Hardly.
Jesus, being God, is omnipresent, meaning that he’s with us in our experience of nature, in our daily lives and in the special moments upon which we reflect. But he’s also a bit harsh about how we’re supposed to ultimately experience his presence. In John 6:53, he says pretty blatantly, “unless you eat the flesh of the Son of Man and drink his blood, you have no life in you.” That’s a little more hardcore than other verses you might have read on Tim Tebow’s eyeblack. As a matter of fact, I’m constantly curious as to how non-Catholic preachers prepare to preach on this passage, a homiletic dodge that has only been around for about 400 or so years.
So how do we figure out how to eat the flesh of Jesus and drink his blood in order to attain eternal life? He’s pretty clear, via the testimony of St. Paul (who very obviously wasn't there when the issue was ordered, but related it to us through oral tradition):
I Corinthians 11:25- “the Lord Jesus on the night when he was betrayed took a loaf of bread, and when he had given thanks, he broke it and said, "This is my body that is for you. Do this in remembrance of me." In the same way he took the cup also, after supper, saying, "This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me."
So what is his body and blood that we have to consume, lest we have no life in us? He pretty much spells it out at the Last Supper.
Aristotelian mental gymnastics, pronouncements from the Council of Trent based on them, and other philosophical efforts are helpful when it comes to defining what we mean by transubstantiation. However, as with most Christian beliefs, an idea such as transubstantiation is not an invention, but more accurately a more concise and practical way to define what Christians such as St. Paul and the Christians with whom he consulted have believed from the beginning.
A final note- Eastern Orthodox Christians do not typically rely on the term “transubstantiation” to articulate their beliefs about the Eucharist. The Reformation didn’t really happen East of Constantinople, so it wasn’t necessary to come up with a word to define what Eastern Christians of good will have believed from the beginning about Holy Communion. When people “horsed around the pool” in their scene (the Eastern lung of the Church), it was more in the areas of atheism, dualism, and Gnosticism (think Stalin). There wasn’t as much of a need to come up with a word for what Christians needed to believe to be considered Christian. They knew what what the Eucharist was in their guts, and knew the stakes of the game. It was worth risking one's life for, as many an Eastern Christian has under many a hostile regime.
"Transubstantiation" may have surfaced as a term relatively recently in Church history, but it is far from being a new concept. And perhaps especially for those who study philosophy, it may be the most adequate way to explain one of the Catholic Church's greatest mysteries.