The spin:
St. Thomas Aquinas, the premier teacher in the Roman Catholic tradition, did not think the early fetus was a person – “ensouled,” in his language. St. Thomas believed the early life in the womb received a spiritual soul – and became a baby – only after three to four months. Thus, embryonic cells in a lab dish or frozen away are certainly not “ensouled.”
The reality
It is true that Aquinas did believe that the soul was not infused at the beginning of a pregnancy. This is because Aquinas followed Aristotle’s embryology (circa 300 B.C.) and believed that an embryo was not formed enough to receive a soul until well into its development. However, 21st century embryology provides clear evidence that everything the soul needs is present from the first moment of every human being’s existence – as numerous Catholic scholars have explained. Aquinas would undoubtedly accept this evidence and agree with the Church’s current teaching.
Further, St. Thomas also believed the intentional ending of a pregnancy at any stage was a sin – regardless of when the soul was present. Thus, he remains firmly within the tradition of the Church in respecting human life at all stages.
More parsing of the original op-ed, later.
Via John Combest.