  For a long time now, confusion has existed in the minds of many over the
meaning of various concepts in thermodynamics. Recently, this point has been
brought to people's attention by two articles appearing on the well-known
archive (arxiv) web site. The content of these two pieces serves to illustrate
many of the problems and has occasioned the construction of this answer to at
least some of them. The position of the axiom proposed by Carath\'eodory is
central in this matter and here its position is clarified and secured within
the framework of thermodynamics. In particular, its relation to the First Law
is examined and justified.
