Words bring us together. Without them, there would be no society, no glue to hold isolated individuals within a linguistic cocoon. But words divide as well: Splitting churches and nations and families. And words have had a major role in dividing the Congress on the subject of stem cell research.

Today marks one year since the House of Representatives voted to approve the Stem Cell Research Enhancement Act. The cosponsors of the Senate version of the bill are now pushing for a vote.

If the act comes up for a vote, it would not be the first time this area of research would be debated in the House or Senate, nor would it likely be the last. Human stem cell research has the potential to revolutionize our understanding of human biology and the treatment of disease, but it also highlights profound moral and religious disagreements. Unfortunately, our choices of words serve to cloak substantive disagreements and create semantically driven disputes that could be avoided with careful attention to the subtleties of our vocabulary.

Misunderstanding surrounds even the definition of a "stem cell." The stem cells of bone marrow, umbilical cord blood, the heart or the brain - typically called "adult stem cells" - do not have the potential to become any cell of the body. They are still called stem cells because they have the potential to become other cells, but their trajectory is limited to a small number of cell types. By contrast, stem cells derived from a human embryo - "embryonic stem cells" - are capable of becoming any cell of the human body given the right conditions.

Even after 30 years of research, successes with adult stem cells have been limited primarily to treatment of some blood cell disorders. Proponents of human embryonic stem cell research should keep in mind that these successes are real and that they demonstrate the utility of adult stem cell research. Similarly, opponents of human embryonic stem cell research should keep in mind that new attempts to derive stem cells from the human embryo will also take many years, but that the resulting stem cells offer a range of possibilities far greater than that for any one type of adult stem cell.

Many opponents and proponents of human embryonic stem cell research note that the central disagreement is about the "moral status" of the human embryo. Opponents of this research will often argue that once an egg is fertilized, the genetic identity of an individual is defined and the proper trajectory for that fertilized egg is a developmental process that will result in an embryo, a fetus, and eventually a newborn child. In this view, the fertilized egg deserves full moral status and therefore protection from any use other than for procreation.

On the other hand, proponents of this research will often recognize moral weight or status for the fertilized egg, but they don't see this as an absolute. While the fertilized egg deserves more consideration than an isolated egg or sperm, it deserves relatively less consideration than the developing embryo, which in turn carries much less moral weight than a developing fetus, or a newborn child.

The issue here is not whether the fertilized egg or embryo has moral status. The issue is whether that status is full and inviolate from the moment of conception or whether it is graded.

Proponents of this research should be aware that many believe that the fertilized egg is a person deserving of full moral consideration. Conversely, opponents of this research will hopefully understand that proponents have not decided to ignore all moral considerations, but that they have concluded that the moral obligation to improve the human condition through research deserves much greater moral weight than the fertilized egg or embryo.

Although there is general understanding of what is meant by "embryo," the terms "pre-embryo" or "blastocyst" are sometimes used to describe early embryonic development. Many opponents of human embryonic research often define all of the earliest developmental stages as embryo; proponents subdivide these stages. Both are talking about exactly the same thing. The real focus should not be on the words, but whether there are significant developmental differences that have moral implications for how we treat this entity,

A final area of concern involves the question of human cloning. Nearly everyone opposes human cloning for reproductive purposes. Scientists propose, however, to derive embryonic stem cells by inserting DNA from the cells of one human into a human egg - a process often called somatic cell nuclear transfer or therapeutic cloning. Whether the resulting artificial zygote is allowed to develop into a blastocyst or not, opponents can be seen as correct in calling this an example of human cloning because even the single cell has a complete copy of the DNA of some other human. For proponents, however, this is not seen as human cloning unless the resulting blastocyst is implanted and allowed to develop.

Because these issues are so divisive, it is unlikely we will soon see agreement about definitions of the words we use. If we hope to make any progress, however, we must recognize that these key terms are used in different senses.

Many of our superficial disagreements are first and foremost misunderstandings. Recognizing this will allow us to focus our attention on the genuine issues of disagreement rather than on semantic disputes about words that confuse and divide citizens, scientists and lawmakers alike.

San Diego Union-Tribune. January 6 2005, p. B9

Michael Kalichman is director of the Research Ethics Programs (http://ethics.ucsd.edu) and professor of pathology in the School of Medicine at the University of California at San Diego (UCSD). He is co-director for the Embryonic Stem Cell Research Oversight Committee at UCSD and has been involved in statewide discussions to address the appropriate ethical review of this research.