Last month's meeting of the International Society for Stem Cell Research in San Francisco witnessed a bizarre semantic debate. Delegates discussed a proposal to refrain from using the term ‘embryo’ when referring to the blastocysts from which human embryonic stem cells are harvested. The scientists involved reject the accusation that they are creating and destroying human lives, and fear that the word ‘embryo’ is a lightning rod that attracts negative scrutiny.

It is true that embryo is an emotive term, but there is little scientific justification for redefining it. Whether taken from a fertility clinic or made through cloning, a blastocyst embryo has the potential to become a fully functional organism. And appearing to deny that fact will not fool die-hard opponents of this research. If anything, it will simply open up scientists to the accusation that they are trying to distance themselves from difficult moral issues by changing the terms of the debate.

At the equivalent meeting last year, the society decided to formally adopt the term ‘somatic cell nuclear transfer’ to describe the procedure in which an adult cell nucleus is transplanted into an egg to produce embryonic stem cells. This procedure had been called ‘therapeutic cloning’ to distinguish it from ‘reproductive cloning’, which would use the same technique in an attempt to make a baby.

But the work is far from yielding any therapies, and scientists realized that the word ‘cloning’ was generating public concern. So they decided to adopt a more technical term less likely to stir up strong emotions. At least that re-branding had the positive effect of toning down the hype surrounding therapeutic cloning.

The name change debated at last month's meeting would be a step too far, however. In the future, researchers may isolate pluripotent stem cells from biological entities that do not have the same developmental potential as embryos. This may justify the creation of a new set of words. Until then, stem-cell biologists should stick to debating the merits and ethics of their work using clear and simple language. They have a strong case to make that will not be helped by playing semantic games in an effort to evade scrutiny.