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These files are maintained strictly for historical reference, research, and recordkeeping purposes, and the content has not been altered or updated since archiving. Content on this site may not meet current digital accessibility standards. If you require an alternative, accessible format of any information found on this site, please contact Bruce Jones, bjones@ucsd.edu to request an accommodation.
Foo Keong,
I am fully supportive of efforts to create a master narrative that
organizes all of the semantic representations of integers into a
coherent scheme. This can be the basis for a curriculum that conveys
something of the systematicity and intellectual rigor of
mathematics. Unfortunately, I've not yet seen that done for integer
operations. Of course, process/object reification--a la Sfard,
Schwartz, Tall, Harel, etc.--is a wonderful resource toward that
effort. But the argument needs to be framed in the particular, not
the general. Although processes cohere into objects which later
participate in higher level processes, these reifications follow
specific trajectories. A classic example is the reification of an
expression as a sequence of instructions (e.g., 3x + 2 meaning take
a number, multiply it by 3, and add 2) into an expression as the
result obtained through that process. As Sfard noted, only in
mathematics does the recipe become the cake. So for the case at
hand, it would be necessary to argue that the process of negation as
take-away compresses into the object of negative as location (for
example on a number line). Even then, the scope of the negation
remains non-symmetric. The negative in 3 × -2 applies to the "2".
The negative in -2 × 3 applies to the 2 x 3 (in the representation I
introduced earlier that we're now discussing).
But I think we're on the same team.
David
-----Original Message-----
From: xmca-bounces@weber.ucsd.edu [mailto:xmca-
bounces@weber.ucsd.edu] On Behalf Of Ng Foo Keong
Sent: Friday, May 01, 2009 2:46 PM
To: eXtended Mind, Culture, Activity
Subject: Re: [xmca] a minus times a plus
So the negative sign in -2 × 3 is being interpreted as a /process/
whereas the negative sign in 3 × -2 is being interpreted as an
/end-product/ (i.e. after taking away the blue chips from the
zero-pairs, you get 2 red chips; -2 = 0 - 2). as an advanced learner
i don't feel that these are different, because (using Anna Sfard's
theory) i have /reified/ the process, compressed it as it were
until i can treat it like an object without any problems. for
a beginner, there is still a very wide gulf between the process
and the end-product.
is there another way out? is it the representation that is the
problem, or should educators put more focus on the learner's
learning experiences?
F.K.
2009/5/1 David H Kirshner <dkirsh@lsu.edu>:
Foo Keong,
Yes, you can increase the semantic span of this approach by
changing the media, as you suggest. But the basic semantic
limitation still applies. The negative sign in -2 × 3 is being
interpreted as a subtraction [-2 × 3 = 0 - (2 x 3)]--very different
from the negative sign in 3 × (-2). Thus the lack of a commutative
interpretation of multiplication in this representation is not
completely solved by arraying markers in a rectangular configuration.
David
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