The heavy toll of AIDS by now outweighs the hypothetical risks of a clean-needle program.

Unfounded concerns about hypothetical risks are far outweighed by the real benefits that will soon be realized, if scientific research and development of genetically modified agriculture is allowed to proceed unhindered.

Why is a hypothetical risk more important than this value?

Gov-ernment and industry officials worry that public discussion of hypothetical risks could trigger unnecessary panic.

On the other hand, he said, if companies and doctors inform all their patients of a hypothetical risk, patients may be hurt just by knowing.

While such safety tests are important, it is possible to become fixated on hypothetical risks that can never be absolutely discounted.

A hypothetical risk of harm is a good reason to investigate efficacy; it is not a good reason to block the introduction of a proved benefit.

"It's a balance between the hypothetical risk of cancer with the risks of not performing an imaging study."

The reasoning was that the nuclear materials will still be suitable for weapons purposes, with the attendant potential or hypothetical risk, of course, of proliferation, after the agreement lapses.

"I'd put my money into basic research, not into chasing hypothetical risks," Dr. Ames said.