Sfard and Linchevski’s (1994) account provided me
with a basis for thinking about the conceptual demands of
different algebraic interpretations but, in the analysis, I intend
Kuchemann’s (1981) wider range of definitions when I refer to
letters. I use the term parameter for numerical givens in
algebraic expressions, yet recognise that parameters can also be
afforded generalised number and variable definitions (Drijvers
and Haarwarden, 2000). However, the higher-level uses were
not relevant to the examples of calculation that I give.