Transcript What we have met before: why individual students

What we have met before:
why individual students,
mathematicians & math educators
see things differently
David Tall
Emeritus Professor in Mathematical Thinking
Platonic
Mathematics
Euclidean
geometry
Geometry
Practical
Mathematics
Space
&
Shape
Conceptual
Embodiment
The Physical World
Platonic
Mathematics
Euclidean
geometry
Blending
Embodiment
&
Matrix Algebra
Symbolism
p
4 = 1- 1 + 1
1
3
...
5 - 7 + ...
Limits
Calculus
Geometry
Graphs
Functions
Trigonometry opp
q
sin
Algebra
= hyp
Arithmetic
Practical
Mathematics
Space
&
Shape
Counting
& Number
Symbolic
calculation &
manipulation
Conceptual
Embodiment
The Physical World
Symbolic
Mathematics
Formal
Mathematics
Axiomatic Formalism
Set-theoretic Definitions & Formal Proof
Set Theory & Logic
Axiomatic Geometry
Platonic
Mathematics
Euclidean
geometry
Axiomatic Algebra, Analysis, etc
Blending
Embodiment
&
Matrix Algebra
Symbolism
p
4 = 1- 1 + 1
1
3
...
5 - 7 + ...
Limits
Calculus
Geometry
Graphs
Functions
Trigonometry opp
q
sin
Algebra
= hyp
Arithmetic
Practical
Mathematics
Space
&
Shape
Counting
& Number
Symbolic
calculation &
manipulation
Conceptual
Embodiment
The Physical World
Symbolic
Mathematics
Axiomatic Formalism
Formal
Mathematics
Formal Meaning
as set-theoretic definition and deduction
Platonic
Mathematics
Embodied
Blending
Meaning embodiment
increasing in
sophistication
from physical
to mental
concepts
Practical
Mathematics
& symbolism
to give
embodied meaning
to symbols
&
symbolic
computational
power
to embodiment
Symbolic
Meaning
increasing power
in calculation
using symbols
as processes to do
& concepts
to manipulate
[procepts]
Symbolic
calculation &
manipulation
Embodiment
The Physical World
Symbolic
Mathematics
Mathematicians can live in the world of formal
mathematics.
Children grow through the worlds of embodiment and
symbolism.
Mathematics Educators try to understand how this
happens.
Fundamentally we build on what we know based on:
Our inherited brain structure (set-before our birth
and maturing in early years)
Knowledge structures built from experiences metbefore in our lives.
The terms ‘set-before’ and ‘met-before’ which work
better in English than in some other languages
started out as a joke.
The term ‘metaphor’ is often used to represent how
we interpret one knowledge structure in terms of
another.
I wanted a simple word to use when talking to
children.
When they use their earlier knowledge to interpret
new ideas I could ask them how their thinking related
to what was met before.
It was a joke: the word play metAphor, metBefore.
The joke worked well with teachers and children:
Set-Befores
Inherited brain structure (set-before our birth and
maturing in early years)
Examples:
Recognising the same object from different angles.
A Sense of Vertical and Horizontal.
Classifying categories such as ‘cat’ and ‘dog’.
… triangle, square, rectangle, circle.
Practising a sequence of actions (see-grasp-suck).
… used in counting …
May be performed
… column arithmetic …
automatically
without meaning
… adding fractions …
… learning algorithms …
Met-Befores
Current ideas based on experiences met before.
Examples:
Two and two makes four.
Addition makes bigger.
Multiplication makes bigger.
Take away makes smaller.
Every arithmetic expression 2+2, 3x4, 27÷9 has an
answer.
Squares and
Rectangles
are different.
Different
symbols
eg
and
represent different thin
Met-Befores
Some are helpful in later learning, some are not.
… works in later situations.
Two and two makes four
Addition makes bigger … fails for negative
numbers.
Multiplication makes bigger
… fails for fractions.
Take away makes smaller
… fails for negative
An algebraic expression
2x+1 does not have an ‘answe
numbers.
Later, by definition, a square is a rectangle.
Different symbols can represent the same thing.
Met-Befores
blended together
In practice, when we remember met-befores, we may
blend together ideas from different contexts.
For instance, numbers arise both in counting and
measuring.
Counting numbers 1, 2, 3, … have much in common
with numbers used for measuring lengths, areas,
volumes, weights, etc.
But they have some aspects which are very different
...
Blending different conceptions of number
Natural numbers build from
counting
1
2
3
4
5
...
The number track ...
Discrete, each number has a next with nothing
between,
starts
counting
at
1,
then
2,
3,
....
The number line builds from measuring
0
1
2
3
4
5
...
The number line ...
Continuous, each interval can be subdivided,
starts from 0 and measures unit shifts to the right.
Blending counting and measuring
Does the difference between number track and
number line matter?
The English National Curriculum starts with a
number track and then uses various number-line
representations to expand the number line in both
directions and to mark positive and negative
fractions and decimals.
Doritou (2006, Warwick PhD) found many children
had an overwhelming preference to label calibrated
lines with whole numbers, with limited ideas that an
interval could be sub-divided.
Their previous experience of whole number
dominated their thinking and the expansion from
number track to number line was difficult for many to
Increasing sophistication of Number Systems
Language grows more sophisticated as it blends
together developing knowledge structures.
Blending occurs between and within different
aspects of embodiment, symbolism and
formalism.
Mathematicians usually view the number systems
as an expanding system:
N
F
Q
R
C
Z
Cognitively the development is more usefully
expressed in terms of blends.
Different knowledge structures for numbers
The properties change as the number system
expands.
How many numbers between 2 and 3?
None
N
Q
Lots – a countable infinity
R
Lots more – an uncountable infinity
C
(the complex numbers are not
None
ordered)
A mathematician has all of these as met-befores
A learner has a succession of conflicting metbefores
From Arithmetic to Algebra
The transition from arithmetic to algebra is difficult for
many.
The conceptual blend between a linear algebra
equation and a physical balance works in simple
cases for many children (Vlassis, 2002, Ed. Studies).
The blend breaks down with negatives and
subtraction (Lima & Tall 2007, Ed. Studies).
Conjecture: there is no single embodiment that
matches the flexibility of algebraic notation.
Students conceiving algebra as generalised
arithmetic may find algebra simple.
Those who remain with inappropriate blends as metbefores may find it distressing and complicated.
Blending different conceptions of number
Real Numbers
as a multi-blend
Embodied
Formal
R
A mathematician
can have a formal
view
Symbolic
A student
builds on
Embodiment & Symbolism
From Algebra to Calculus
The transition from algebra to calculus is seen by
mathematicians as being based on the limit concept.
For mathematicians, the limit concept is a metbefore.
For students it is not.
A student can see the changing steepness of the
graph and embody it with physical action to sense
the changing slope.
slope zero
slope –
slope +
Calculus
Local straightness is embodied:
You can see why the derivative of cos is minus sine
Calculus
Local straightness is embodied:
You can see why the derivative of cos is minus sine
The graph of sine
upside down....
slope is – sin x
Calculus
Local straightness is embodied:
E.g. makes sense of differential equations ...
Reflections
As we learn, our interpretations are based on
blending met-befores, which may cause conflict.
Learners who focus on the powerful connections
between blends may develop power and flexibility,
those who sense unresolved conflict may develop
anxiety.
Mathematicians have more sophisticated metbefores and may propose curriculum design that
may not be appropriate for learners.
It is the job of Mathematics Educators (who could
be Mathematicians) to understand what is going on
and help learners make sense of more
sophisticated ideas.