Distinctions that require explanations tend to get lost in public debate, and the controversy over cloning is a perfect example.

There are two fundamentally different types of cloning — "reproductive cloning" and "therapeutic cloning" — but the distinction between them is in danger of getting lost. And if it does, it could be a severe blow to science.

The press and scientists have been careful in every report to explain that reproductive cloning refers to the creation of an embryo using a technique known as somatic cell nuclear transfer. In this process, the nucleus of the cell from an adult is transferred into an egg whose own nucleus has been removed. The goal is to bring the embryo to term and produce a live baby.

The explainers of science have also been careful to spell out the ways in which therapeutic cloning differs from its counterpart. In this process, an embryo is created through the same technique, but with the goal of extracting stem cells from it and producing — someday, hopefully — new medical therapies.

Of course, the fact that these explanations must be given over and over only shows how badly the distinction has failed to take root with the public.

As the controversy has heated up with the claim of the first human clone, the word cloning has come to mean, in the public's mind, the use of somatic cell nuclear transfer for artificial, asexual reproduction; to make a biologic copy of an existing organism. Scientists themselves often use the word "cloning" casually to refer to any use of somatic cell nuclear transfer. But elsewhere in science, cloning refers to outcome rather than process: it denotes replication of some biologic entity — perhaps an organism, but perhaps only one cell, or perhaps just a stretch of DNA. This reproduction might involve somatic cell nuclear transfer, or it might use some other technology.

The difficulty in making a distinction between reproductive and therapeutic cloning is showing up most evidently in two competing Senate bills. One, supported by Senator Bill Frist, the new majority leader, would ban all cloning research. The other, with bipartisan support, views cloning via its end result, and would allow therapeutic cloning while banning reproductive cloning.

Words are not always content with scientists' definitions of them. What percentage of Americans actually think of a tomato as a fruit rather than a vegetable? How often are bison called buffalo? In general, we can live with that sort of confusion — but when it comes to a politically charged issue like cloning, we can't.

So it might make sense for scientists to restrict their use of the word cloning to the reproductive type. This is exactly what Stanford University did when it denied that studies it planned to sponsor on somatic cell nuclear transfer would be cloning research. Scientists would only be creating stem cells, said university officials, not doing cloning. The claim was preposterous by scientific standards — that is, if cloning is defined by a laboratory technique. But if by "cloning" we mean a form of reproduction, it was exactly right.

Of course, only scientists themselves can decide how they will use their terms of art. A more vexing problem is what the rest of us should do. Even if the public understands the scientific differences between types of cloning, I have my doubts that it will be enough. People are still likely to see therapeutic cloning as derivative from reproductive cloning: it starts the same way, although the process is interrupted and the new organism is put to other uses. Thus we will view therapeutic cloning with a tinge of the apprehension that reproductive cloning arouses in us, and a total ban on cloning correspondingly will grow more attractive.

Perhaps in the end scientists should let the public use the word cloning in the sense it wants to and focus instead on making the distinction between cloning and stem cell research. Both processes can, at certain stages, employ the same laboratory techniques, but then they follow different paths and have different outcomes. And in this case, it is outcomes, not laboratory techniques, that matter.

Gregory E. Kaebnick is a research associate at The Hastings Center, a research institute in bioethics.

Now, the one idea that most folks don't seem to be able to hold in their mind is that, for example, if I make a clone of myself, it will be a blank slate of mind, without any of my life's experiences.

It will not be a copy of me that many science fiction movies portray.

It will, with luck, be able to avoid or be shielded from some of the personality-affecting traumas which I endured as I grew up, but the odds are that it will also be subject to the same weaknesses, allergies, and physical problems that I've dealt with in my life, and many that I may have to deal with in the future.

Science is nowhere near the point of being able to insure that those problems or weaknesses can be prevented or eliminated, although I'd vote for the possibility, if it were offered.

Try to remember that. The clone is not you; it's a copy of you as an infant. All the rest is new. Everything that happens to it after birth [and before!] is new and different. The results are not guaranteed.