When An Ecologist Warns That We Are Using Up Irreplaceable Natural Resources And An Economist Rejoins That Ingenuity And Enterprise Will Find Substitutes For Most Resources, What Underlying Premises And Definitions Shape Their Arguments?

The ecologist is assuming that there are no replacements for these resources and that technology will not necessarily fill the void. His/her premise does not include the possibility of substitutes, much the same as the extinction of a species. The economist looks at past occurrences   and assumes such breakthroughs will continue due to economic pressure (increased commodity price=increased innovation) This is probably the most realistic view based on modern history. He/she is assuming that there is some substitute/alternative but is relying on past case histories to predict the future, which is logical but not always correct.