St. Thomas also held that contraception was wrong, not merely abortion, so the fact that ensoulment didn't happen before quickening (in his learned opinion) did

St. Thomas also held that contraception was wrong, not merely abortion, so the fact that ensoulment didn't happen before quickening (in his learned opinion) didn't change his understanding of how moral contraception and abortion are (he believed they were both gravely sinful). St. Thomas said ensoulment happened at quickening because the science of the time said that the zygote was a simple thing. Given that understanding, St. Thomas held that the rational soul was not necessary to explain the developments that happened and in fact, that the soul which animated such simple matter must be simpler. Modern science tells us that the zygote is anything but simple and so St. Thomas' objection on the basis of a "simple" material component are incorrect. St. Thomas also said that all that he had ever written was "so much straw" after receiving a mystical experience of God's love (not _wrong_, just completely inadequate).