Probably the most famous argument against the pro-life position is Judith Jarvis Thomson’s Violinist Analogy, in which you are attached, against your will, to a famous unconscious violinist to prevent his dying from a kidney ailment. I have already responded to the violinist analogy in previous articles. But within the original essay where the violinist argument appeared, A Defense of Abortion, there are also other arguments against the pro-life position. I would like to take a look at the entirety of her essay and show why it doesn’t stand up to scrutiny. I’ll look at it in sections, divided up as she divided her original essay.
Thomson immediately talks about the majority of pro-life arguments, which rely on the fact that the unborn is a human being, a person, from conception. I do find it ironic that she, a professional philosopher, would say that our arguments for that are not argued well, and we accept them uncritically, but then uses one of the worst analogies that pro-choice people use to illustrate that. She says that acorn development is similar to human development, but it does not follow that acorns are oak trees. For why this reasoning fails, see these two articles.
She argues that to place a line on the “slope” of human development as to where it is now considered a person commits the “slippery slope fallacy,” but like most fallacies it is not always a fallacy. As long as there is warrant for it, then it is not a fallacious argument. It is not fallacious to argue that a fetus five minutes from being born is fundamentally no different than a newborn five minutes after being born. The only difference between the two is the birth event, and there is nothing mystical about the birth event that suddenly grants personhood or “humanity.” If you’re going to draw a line, then you need a strong enough argument as to why the line should be drawn there and not five minutes, five hours, or even five days before.
She then asserts that it is not clear how we get from “the unborn is a person” to the impermissibility of abortion. I’m surprised a professional philosopher can’t see it, but if we have the premise “it is immoral to kill a person without strong justification”, then it is easy to get to the conclusion “abortion is immoral without strong justification.” Any reason that would be immoral to kill someone outside the womb would also be immoral to kill someone inside the womb.
So Thomson claims to accept the pro-life person’s premise that the unborn are persons from conception, but as Frank Beckwith points out, she’s really not making this concession. He writes, “What Thomson is granting, then, is a view of personhood consistent with the pro-life position only insofar as it is aligned with a minimalist understanding of autonomy and choice. That view isolates the individual from other persons -- generationally, contemporaneously, and institutionally -- except as those relationships arise from the individual’s explicit choice. But that is not the pro-life view of personhood.
“The pro-life view is that human beings are persons-in-community and have certain obligations, responsibilities, and entitlements as members of their community that arise from their roles as mother, father, child, sibling, citizen, neighbor, etc. These roles are informed by institutions and ways of life that arose over time to account for, among other things, one’s proper relationship to others, which depends on a person’s degree of development (i.e. whether or not one is a child or an adult), the geographical proximity of those with whom one shares a common life, and what we owe those who cannot care for themselves due to age or infirmity. This also includes one’s responsibility for protecting and nurturing vulnerable and defenseless human beings who come into being as a result of one engaging in generative acts that have the intrinsic purpose of bringing such beings into existence” (emphasis in original).
Thomson is not granting our minor premise because her article assumes that human beings have no moral obligations toward each other, or at least only obligations that are chosen. But people have all sorts of responsibilities thrust upon them without free choice. Parents are expected to take care of their children, even when they don’t want to. That obligation does not begin at birth.
Here Thomson goes into her famous analogy of the violinist. I have critiqued this specific argument in the past, and a wealth of articles have been written critiquing it in print and on-line, so I won’t go into that here, save a few remarks that I think are valuable to keep in mind. 
John T. Wilcox argues that the weirdness of the violinist analogy (and Wilcox tells us that weird is a technical term, and does not use it in any way to minimalize the unique aspects of pregnancy) and the commonality of pregnancy “is significant. Some people try to look at this matter very abstractly, and say that right is right, whether it happens one time or billions of times; but in a serious sense, something that happens all the time and is necessary is different, by virtue of that fact, from what is rare or impossible. So it will be plausible to regard them differently from an ethical point of view. It is at least arguable, and many theorists believe, that the moralities we have represent some ways of dealing with the realities and and regularities of human life; and they may not fit well the irregularities or impossibilities. Our teaching methods, when they work, fit the kinds of students we ordinarily have; they might not be suitable for Martians or Venusians. And vice versa. Similarly for our moral principles. So what is appropriate for kidnapped kidney bearers and their violinist parasites might not be appropriate for mothers and the babies in their wombs.” 
While we can’t ordinarily dismiss an analogy simply because it’s weird, I think there’s a lot of merit to Wilcox’s argument. Our moral obligations may be different in a normal situation like pregnancy than in a case of abduction and being forced into a medical situation like being “plugged in” to a famous violinist. The fact that the situation with the violinist is essentially a medical impossibility may confuse our intuitions on the topic.
As I indicated in my last article, the responsibility objection is the most powerful objection to the violinist analogy. In fact, pro-life philosopher Trent Horn talks about a thought experiment he devised with his colleague Tony George, based on Thomson’s violinist analogy. He says, “imagine you wake up in a hospital and you’re connected to Thomson’s violinist. You decide, ‘you know what? It would be nice to stay plugged in but I’m going to unplug from this guy. I can’t stay here for nine months.’ So you unplug, you start to walk out of the hospital, and start to feel really nauseous and light-headed. The director of hospital runs in and says, ‘oh my goodness! Plug back in or you’ll die!’ So you scramble into the bed and you plug in to the guy. The director says this to you: ‘I”m terribly sorry, but last night you were kidnapped by the Society of Musical Pranksters (unlike Thomson’s Society of Music Lovers). And these Pranksters, of which the violinist is a member, have a lot of fun together. But because they’re pranksters, every now and then they’ll end up plugged into an innocent person. And when that happens, it destroys the innocent person’s kidneys. But don’t worry. If you stay plugged in to the violinist in nine months your kidneys will heal, and then you can go on your way.’ And you pass out, because this is just crazy.
“The violinist wakes up. He looks over at you and says, ‘hey...he doesn’t have a right to use my body without my consent. I’m not going to let him use my kidneys without my permission.’ He unplugs from you, walks out of the hospital, and you die of kidney failure and you’re thrown into the hospital incinerator. Now the question is does the violinist in that case have the right to unplug from you?”  As Trent points out, it seems strange to suggest that the violinist, who is a member of the Society of Musical Pranksters, has the right to unplug from you, since he’s the reason you’re in the predicament in the first place. He’s responsible for you needing that life support.
In fact, Trent mentions that philosopher Peter Unger has shown that thought experiments sometimes twist our moral intuitions based on the point of view we have in the experiment. Thomson's violinist analogy is from the perspective of the pregnant woman. But Tony and Trent’s Reverse Violinist thought experiment is from the perspective of the unborn child.
Now admittedly, the responsibility objection to Thomson’s violinist does not work in the case of rape. In fact, Thomson even mentions as much. She concedes that the analogy works because you’re kidnapped (which is more analogous to the case of rape), and goes on to state, “Surely the question of whether you have a right to life at all, or how much of it you have, shouldn’t turn on the question of whether or not you are a product of a rape.” I wholeheartedly agree, which is why I believe abortion to be immoral even in the case of rape. However, there are pro-life people who argue that abortions can be justified in the case of rape specifically because of bodily rights, and the position that if you consent to the act of sexual intercourse, you waive your right to bodily autonomy. Thomson doesn’t take this potential objection into consideration.
Thomson then suggests that pro-life people would not make an exception for a woman who must stay in bed for the entire pregnancy, or for a woman whose pregnancy, miraculously, lasted nine years or the rest of her life. I think that extending the length of pregnancy in this example is utterly unhelpful. The reality is that a woman isn’t pregnant for her entire life, nor could she ever be. In fact, this is one way in which Thomson confuses intuitions. To the medical community, an abortion just is the act of expelling the separation of the fetus from the mother. As Bernard Nathanson has noted, “The fundamental misunderstanding here corrupts the entire debate. Though in practice death has become the aim as well as the result of separating the fetus, the medical term does not imply any intent to destroy it.”  If the pregnancy were to stretch out too long, the doctor could simply remove the fetus intact and, presumably, healthy. Considering that later in her essay she indicates that the right to an abortion does not entail the right to the fetus’ death, this is particularly puzzling.
When it comes to a more extreme medical case, such as the mother being bedridden, I am not sure this would be grounds for killing the human fetus. As Dr. Nathanson argues, “In morality, life can only be equated with life, not with convenience or sociology or politics or economics or poverty...In arguing an issue of life, one can only invoke issues of life to counterbalance it.” 
Her last paragraph of the introduction references pro-life advocates who do not believe abortion is justified even to save the mother’s life. I believe that abortions in those cases are morally justified, so I don’t need to respond to that particular point.
In the interest of space, I’ve only critiqued the introduction here. I’ll try to critique as many of the individual sections as possible in each part of this series. The violinist was just the tip of the iceberg. Later in her essay, she uses even more bizarre scenarios in an attempt to justify abortion, but so far Thomson’s essay is not off to a very promising start.
 See also Frank Beckwith’s books Politically Correct Death and Defending Life, as well as Christopher Kaczor’s The Ethics of Abortion.
 John T. Wilcox, Nature as Demonic in Thomson’s Defense of Abortion, from The Ethics of Abortion: Pro-Life vs. Pro-Choice, Third Edition, ed. by Robert M. Baird and Stuart E. Rosenbaum, (Prometheus Books: Amherst, New York, 2001), p. 260.
 The relevant section starts at about 6:45 on the video.
 Bernard N. Nathson, M.D., with Richard N. Ostling, Aborting America, (Doubleday: New York, 1979), p. 177.
 ibid., p. 240.