The library's note
The first premise — that whatever begins to exist has a cause — most people grant readily; things do not simply pop into being uncaused. The weight falls on the second: that the universe itself had a beginning, a first moment, rather than stretching back forever.
Al-Ghazali argued for it on philosophical grounds: an actually infinite series of past events, he held, is impossible — you could never have "arrived" at the present moment by crossing an endless past. Craig adds a scientific support: standard Big-Bang cosmology describes a universe with a finite age, beginning some fourteen billion years ago. Both supports are contested — critics such as Wes Morriston and Graham Oppy argue that an infinite past involves no real contradiction, and the cosmology is a live scientific question, not a closed one. On the physics, this library takes no side; it points to the literature.
The argument's hosted heart here is a medieval disagreement between two saints. Bonaventure held that reason can demonstrate the world had a beginning. Thomas Aquinas thought otherwise, and his reasons matter. Though he firmly believed, as a matter of faith, that the world began, he held that this cannot be established by philosophy at all: the beginning of the universe leaves no trace in the timeless natures of things, and God's free choice to create when he did is not something reason can reconstruct. Whether the world had a first moment, on his view, is settled by revelation — and is otherwise a question for observation, not for metaphysics.
He had, too, a methodological caution that reads as strikingly modern: do not rest the faith on arguments that cannot be made to hold, "lest anyone, presuming to demonstrate what is of faith, should bring forward reasons that are not cogent, so as to give occasion to unbelievers to laugh." On his view the kalam tries to prove more than reason can deliver, and by overreaching it hands critics an easy target. It is a striking thing to host: a Doctor of the Church declining to use an argument for God because he judged it could not be made to work.
That caution shaped his own approach. Aquinas built his Five Ways so as not to depend on a beginning at all — they argue from the world's present, here-and-now dependence, and would go through even if the universe were eternal. It is precisely this that separates them from the kalam, which stands or falls on whether the universe began. So the argument sits at an unusual crossing: its founding statement is out of our reach in English, its decisive premise now turns on cosmology, and its sharpest medieval critic was a canonized theologian who thought it claimed too much. Its liveliest form today is Craig's, debated across contemporary philosophy of religion — followed here by link, since it too is under copyright.
Written for this library — not a quoted source. It reports how the premise is argued and answered; the philosophers' own words are above.