If you’ve read the Supreme Court’s ruling in Hobby Lobby or the reaction to it, then you know what sparked the lawsuit. The Affordable Care Act says that employer-provided insurance must include essential health benefits, including all medically authorized forms of contraception. The owners of Hobby Lobby objected to this requirement, because they believe that four common forms of birth control—two versions of the “morning-after pill” and two kinds of intrauterine devices (IUDs)—are “abortifacients.” In other words, the owners of Hobby Lobby think these contraceptives end pregnancies rather than prevent them. And they believe that is tantamount to ending a life.

The claim, which you can find on virtually any conservative website, has been making the rounds for a long time. It’s stuck because the science on how these particular drugs and devices work wasn’t that great. But recent advances in medical diagnostics and some ingenious studies have changed that. We know a lot more about how the contraceptives work. We can be very confident that three of the four contraceptives do not lead to abortion, even using the conservative definition of when life begins, and we can be almost (although not quite) as sure that the fourth does not, either.

There are essentially six ways to prevent pregnancy:

Make the cervical mucus inhospitable (sperm can’t get to the egg) Inhibit ovulation (prevent the release of an egg) Affect fertilization (the ability of the sperm to meet up with and/or penetrate the egg). Affect the fertilized egg (prevent implantation) Create an inhospitable uterine environment (prevent implantation) Affect the implanted embryo

As far as the medical establishment is concerned, pregnancy doesn’t begin until implantation. (In fact, 80 percent of fertilized eggs never implant.) So under this “medical” definition of pregnancy, only method #6—that is, doing something to the implanted embryo—would constitute a form of abortion. But religious conservatives hold that pregnancy and life itself begin at the moment an egg is fertilized. Under the “religious” definition of pregnancy, methods 4, 5 and 6 would all constitute forms of abortion.

What does that mean for the four types of contraception at issue in the Hobby Lobby case? Let’s consider each one.