Uncertainty spreads through our lives so thoroughly that it dominates our language，Our everyday speech is made up in large part of words like probably, many, soon,great,little.What do these words mean? Such verbal imprecision is not necessarily to be criticized. Indeed, it has a value Just because it allows uw to express judgments when a precise quantitative statement is out of the question. We have been trying to pin down by experiments what people meari by these expressions in specific contexts, and how the meanings change with age. For instance,a subject is told There are