guershon harel
TRANSCRIPT
Two Fundamental Questions: A DNR Perspective
Guershon HarelUniversity of California, San Diego
http://www.math.ucsd.edu/~harel
Two Fundamental Questions
1. What mathematics should we teach in school?
2. How should we teach It?
DNR-based Instruction in Mathematics
What is DNR?DNR is a system of three categories of constructs:
– Premises: explicit assumptions, most of which are taken from or based on existing theories.
– Concepts: definitions oriented within the stated premises.
– Claims: statements formulated in terms of the DNR concepts, entailed from the DNR premises, and supported by empirical studies.
• Instructional principles: claims about effects of teaching
practices on student learning.
The term DNR refers to three foundational instructional principles:–The Duality Principle–The Necessity Principle–The Repeated Reasoning Principle
DNR Premises
Mathematics 1. Mathematics: Knowledge of mathematics consists of all ways of understanding and
ways of thinking that have been institutionalized throughout history.Learning
2. Epistemophilia: Humans—all humans—possess the capacity to develop a desire to be puzzled and to learn to carry out mental acts to solve the puzzles they create. Individual differences in this capacity, though present, do not reflect innate capacities that cannot be modified through adequate experience. (Aristotle)
3. Knowing: Knowing is a developmental process that proceeds through a continual tension between assimilation and accommodation, directed toward a (temporary) equilibrium. (Piaget)
4. Knowing-Knowledge Linkage: Any piece of knowledge humans possess is an outcome of their resolution of a problematic situation. (Brousseau)
5. Context-Content Dependency: Learning is context and content dependent. (Cognitive Psychology)
TeachingTeaching
6. Learning scientific knowledge (such as mathematics) is not spontaneous. There will always be a difference between what one can do under expert guidance or in collaboration with more capable peers and what he or she can do without guidance. (Vygotsky)
Ontology 7. Subjectivity: Any observations humans claim to have made is due to what their
mental structure attributes to their environment. (Piaget)8. Interdependency: Humans’ actions are induced and governed by their views of the
world, and, conversely, their views of the world are formed by their actions. (Piaget)
DNR Premises
Mathematics 1. Mathematics: Knowledge of mathematics consists of all ways of understanding and
ways of thinking that have been institutionalized throughout history.
Learning 2. Epistemophilia: Humans—all humans—possess the capacity to solve puzzles
AND to develop a desire to be puzzled. (Aristotle)
Individual differences in this capacity, though present, do not reflect innate capacities that cannot be modified through adequate experience.
3. Knowing: Knowing is a developmental process that proceeds through a continual tension between assimilation and accommodation, directed toward a (temporary) equilibrium. (Piaget)
4. Knowing-Knowledge Linkage: Any piece of knowledge humans possess is an outcome of their resolution of a problematic situation. (Brousseau)
5. Context-Content Dependency: Learning is context and content dependent. (Cognitive Psychology)
Teaching6. Learning scientific knowledge (such as mathematics) is not spontaneous. There will always be a
difference between what one can do under expert guidance or in collaboration with more capable peers and what he or she can do without guidance. (Vygotsky)
Ontology 7. Subjectivity: Any observations humans claim to have made is due to what their mental structure
attributes to their environment. (Piaget)
8. Interdependency: Humans’ actions are induced and governed by their views of the world, and, conversely, their views of the world are formed by their actions. (Piaget)
Subject MatterConceptual Tools
DNR-Based Instruction in Mathematics
DNR-Based Instruction in Mathematics
DualityDuality
NecessityNecessity
Repeated ReasoningRepeated Reasoning
Instructional Principles
The Necessity Principle
For students to learn the mathematics we intend to teach them, they must have a need for it, where ‘need’ refers to intellectual need, not social or economic need.
D N R
DNR in the Classroom
• What does it mean to think of mathematics teaching and learning in terms of both ways of understanding and ways of thinking?
• How does DNR is used to advance desirable ways of understanding and ways thinking with students?
• When should one start targeting particular ways of thinking with students?
Rectangular Land ProblemA farmer owns a rectangular piece of land. The land is divided into four rectangular pieces, known as Region A, Region B, Region C, and Region D, as in the figure:
One day the farmer’s daughter, Nancy, asked him, what is the area of our land? The father replied:
I will only tell you that the area of Region B is 200 larger than the area of Region A; the area of Region C is 400 larger than the area of Region B; and the area of Region D is 800 larger than area of Region C.
What answer to her question will Nancy derive from her father’s statement?
A
B
C
D
Please work individually on this problem
What are some of the assumed ways of thinking?
What are some of the targeted ways of thinking?
Assumed Way of Thinking:The problem-solving approach of representing a given problem algebraically and applying known procedures (such as procedures to solve systems of linear equations) to obtain a solution to the problem.
Algebraic representation approach
Objective 1:Reinforce this way of thinking.
Problem solving approaches constitute one category of ways of thinking.
How do we help students acquire the algebraic representation approach way of thinking?
The Lesson: Actual Classroom Episodes
• Students’ responses– Explanations in terms of
• students current knowledge• the way students have been taught• nature of learning
• Teacher’s actions– Explanations in terms of
• the teacher’s conceptual framework: DNR-based instruction in mathematics
Students’ ResponsesAll students translated the farmer statement into a system equations similar to:
Attempted to construct a 4th equation, e.g.,
200
400
800
B A
C B
D C
( 200) ( 400) ( 800)B C D A B C
Students’ Responses
Attempted to construct a 4th equation, e.g.,
Explanation of students’ behavior:Most students’ conception of a system of equations includes the constraints:
• the number of unknowns must equal the number of equations.
• there is always one solution.
These are largely didactical obstacles: obstacles caused by how students are taught.
didactical obstacles versus
epistemological obstacles
( 200) ( 400) ( 800)A C D A B C
DNR Premises
Mathematics 1. Mathematics: Knowledge of mathematics consists of all ways of understanding and
ways of thinking that have been institutionalized throughout history.Learning
2. Epistemophilia: Humans—all humans—possess the capacity to solve puzzles AND to develop a desire to be puzzled. (Aristotle)Individual differences in this capacity, though present, do not reflect innate capacities that cannot be modified through adequate experience.
3. Knowing: Knowing is a developmental process that proceeds through a continual tension between assimilation and accommodation, directed toward a (temporary) equilibrium. (Piaget)
4. Knowing-Knowledge Linkage: Any piece of knowledge humans possess is an outcome of their resolution of a problematic situation. (Brousseau)
5. Context-Content Dependency: Learning is context and content dependent. (Cognitive Psychology)
Teaching6. Learning scientific knowledge (such as mathematics) is not spontaneous. There will
always be a difference between what one can do under expert guidance or in collaboration with more capable peers and what he or she can do without guidance. (Vygotsky)
Ontology 7. Subjectivity: Any observations humans claim to have made is due to what their
mental structure attributes to their environment. (Piaget)8. Interdependency: Humans’ actions are induced and governed by their views of the
world, and, conversely, their views of the world are formed by their actions. (Piaget)
Subject MatterConceptual Tools
Teacher’s action 1: classroom discussion of the students’ proposed solution
Outcome: Agreement: there are infinitely many solutions:
every choice of A gives a value for the total area.
200
400
800
B A
C B
D C
200 400( ) ( ) ( )
4 2
0
200
8 0
Tot B Cal A
A
r
B
e
A
Da A
A
C
– Explanations of the teacher’s action in terms of DNR
• Teaching actions in DNR are determined largely by students’ current knowledge.Teacher’s actions depends on the solutions proposed, consensus or dispute among students about a particular solution or idea, etc.
Agreements and disputes must be explicitly institutionalized in the classroom.
• Public Debate versus Pseudo-Public Debate.
Teacher’s action 1: classroom discussion of the students’ proposed solutionOutcome:
Agreement: there are infinitely many solutions: every choice of A gives a value for the total area.
Total Area = 4A + 2200
What can and should the teacher do with this outcome?
DNR’s Approach:Present the student with a new task that puts them in a disequilibrium.
Teacher’s Action 2Construct two figures, each representing a different solution.
200
400
800
B A
C B
D C
200 400( ) ( ) ( )
4 2
0
200
8 0
Tot B Cal A
A
r
B
e
A
Da A
A
C
Students’ Response
200
400
800
4 2200
B A
C B
D C
Total Area A
100
300
700
1500
5
20
15
140
140×15≠1500
Students’ Response
200
400
800
4 2200
B A
C B
D C
Total Area A
100
300
700
1500
10
10
30
70
70×30≠1500
Teacher: you didn’t try fractions
200
400
800
4 2200
B A
C B
D C
Total Area A
100
300
700
1500
2/3
100÷2/3=150
2
700÷2/3=1050
1050×2≠1500
Teacher: you didn’t try irrational numbers
200
400
800
4 2200
B A
C B
D C
Total Area A
100
300
700
1500
√2
100÷√2
300÷(100÷√2)=3×√2
700÷√2
(3×√2) × (700÷√2) ≠1500
Conjecture: The figure cannot be constructed for A=100
Teacher’s action-students’ response 3:Prompted by the teachers, some students offered to use a variable t.
• Students were brought to a conceptual stage where the use of variable was necessitated intellectually
–it was a natural extension of their current activity.
• Conjecture was settled for the students (i.e., proved) by algebraic means.
100
300
700
1500
t
100÷t
300÷(100÷t)=3t
700÷t
3t×(700÷t)=2100≠1500
Students’ Responses
• Surprise– Almost a disbelief
• Formation of a second conjecture– It doesn’t work with A=100; perhaps it would work with a different
value of A.• Trial-and-error approach repeated
– Students try different values for A, but ran into the same conflict: none of the values chosen led to a constructible figure.
100
300
700
1500
t
100÷t
300÷(100÷t)=3t
700÷t
3t×(700÷t)=2100≠1500
Teacher’s action 4: Discussion: How to resolve the question of whether the figure is constructible for any values of A.
The class, led by the teacher, repeats the same activity with the variable A.
A
A+200
A+600
A+1400
t
A÷t
(A+200)÷(A÷t)=
(A+200)t/A
(A+600)÷t
2 2
( 200) 6001400
800 12000 1400
12000 600
200
A t AA
A t
A A A A
A
A
Outcomes:
•Students were brought—again—to a conceptual stage where the use of variable was necessitated intellectually.
•Second conjecture was settled for the students (i.e., proved)—again—by algebraic means.
DNR-Based Instruction in Mathematics
DNR-Based Instruction in Mathematics
DualityDuality
NecessityNecessity
Repeated ReasoningRepeated Reasoning
Instructional Principles
Teacher’s action 5: Reflective discussion:
• Why did our first approach to solving the problem fail?• The need to attend to the figure’s form:
versus
Objective 2:• To advance the way of thinking:
In representing a problem algebraically, all of the problem constraints must be represented.
A
B
C
D
A
CB
D
SummaryWhat are the ways of thinking targeted by this Lesson?
Ways of Thinking:1. In representing a problem algebraically, all of the problem
constraints must be represented.
2. Algebraic representation way of thinking: Reinforcing the problem-solving approach of representing a given problem algebraically and applying known procedures (such as procedures to solve systems of linear equations) to obtain a solution to the problem.
Problem solving approaches constitute one category of ways of thinking.
3. Mathematics involves trial and error and proposing and refining conjectures until one arrives at a correct result.
Beliefs about mathematics constitute the second category of ways of thinking.
4. Algebraic means are a powerful tool to remove doubts—that is, to prove or refute conjectures.
Proof schemes (how one removes doubts about mathematical assertions) constitute the third category of ways of thinking.
Concepts learned/reinforced through intellectual need: to solve a problem—reach an equilibrium
• Operations with fractions and irrational numbers
• Algebraic manipulations
• The concepts of variable and parameter
Intellectual Need versus Intrinsic Motivation
Intrinsically motivated activities are defined as those that individuals find interesting and would do in the absence of operationally separable consequences.
Intrinsic motivation is conceptualized in terms of three innate psychological needs:
Need for autonomy
Need for competence
Need for relatedness
Intrinsic Motivation
Need for autonomy:The need for freedom to follow one’s inner interest rather than being control by extrinsic rewards.
Need for competence:The need for having an effect—for being effective in one’s interactions with the environment.
Need for relatedness:The need for a secure relational base with others.
Intellectual Need
Intellectual need refers to the perturbational stage in the process of justifying how and why a particular piece of knowledge came into being.
It concern the genesis of knowledge, the perceived a priori reasons for the emergence of knowledge.
Categories of intellectual need(a) Need for certainty
(b) Need for causality (enlightenment)
(c) Need for computation
(d) Need for communication-formulation-formalization
(e) Need for structure
Goal: To necessitate the e-N definition of limit
Teacher: What is and why?
Students:
Teacher:
1limn n
1 1lim 0 because the larger gets the closer is to zero.n
nn n
5 10
4
2
-2
-4
f x = -1
1 1lim 1 because the larger gets the closer is to -1.n
nn n
Algebraic approach way of thinking: Reinforcing the problem-solving approach of representing a given problem algebraically and applying known procedures (such as procedures to solve systems of linear equations) to obtain a solution to the problem.
Need for ComputationTowns A and B are 300 miles apart. At 12:00 PM, a car leaves A toward B, and a truck leaves B toward A. The car drives at 80 m/h and the truck at 70 m/h. When and where will they meet?Students’ reasoning:After 1 hour, the car drives 80 miles and truck 70 miles. Together they drive 150 miles.In 2 hours they will together drive 300 miles.Therefore, They will meet at 2:00 PM.They will meet 160 miles from A.
Towns A and B are 300 miles apart. At 12:00 PM, a car leaves A toward B, and a truck leaves B toward A. The car drives at 80 m/h and the truck at 70 m/h. When and where will they meet?
Towns A and B are 300 100 miles apart. At 12:00 PM, a car leaves A toward B, and a truck leaves B toward A. The car drives at 80 m/h and the truck at 70 m/h. When and where will they meet?
Students’ reasoning:It will take them less than one hour to meet.
It will take them more than 30 minutes to meet.
They will meet closer to B than to A.
Let’s try some numbers:
?50 5080 70 100
60 60
?40 4080 70 100 ( !)
60 60Yes
Towns A and B are 118 miles apart. At 12:00 PM, a car leaves A toward B, and a truck leaves B toward A. The car drives at 80 m/h and the truck at 70 m/h. When and where will they meet?
Students’ reasoning:It will take them less than one hour to meet;It will take them more than 30 minutes to meet; They will meet closer to B than to A. Let’s try some numbers:
50 50
60 6
?
80 70 180
1
40 40
60 6
?
80 70 180
1
Repeated
Reasoning
Necessitating the concept of variable
30 30
60 6
?
80 70 180
1
Local Necessity versus Global Necessity
First Course in Linear Algebra• Focus: Linear systems—scalar and differential• The problem (general investigation):
Given a linear system1. How do we solve it?
2. Can we solve it efficiently?– Is there an algorithm to solving such systems?
3. How do we determine whether a given system has a solution?
4. If a system is solvable, how many solutions does it have?
5. If the system has infinitely many solutions, how do we list them?
Necessitating Deductive Reasoning
Students and Teachers’ Conceptions of Proof: Selected Results
• Students and teachers justify mathematical assertions by examples
• Often students’ and teachers’ inductive verifications consist of one or two example, rather than a multitude of examples.
• Students’ and teachers’ conviction in the truth of an assertion is particularly strong when they observe a pattern.
• Students view a counterexample as an exception—in their view it does not affect the validity of the statement.
• Confusion between empirical proofs and proofs by exhaustion.
• Confusion between the admissibility of proof by counterexample with the inadmissibility of proof by example.
Teaching Actions with Limited Effect
– Raising skepticism as to whether the assertion is true beyond the cases evaluated.
– Showing the limitations inherent in the use of examples through situations such as:
The conjecture “ is an integer” is false for . The first value for which the statement is true is: 30,693,385,322,765,657,197,397,208
21141 1y 251 10y
Why showing the limitations inherent in the use of examples is not effective?
• Students do not seem to be impressed by situations such as:
• The conjecture “ is an integer” is false for . The first value for which the statement is true is: 30,693,385,322,765,657,197,397,208
• Students view a counterexample as an exception—in their view it does not affect the validity of the statement.
21141 1y 251 10y
How Do We Intellectually Necessitate the Transition from Empirical Proof Schemes to
Deductive Proof Schemes?
A Dissertation Topic!
Linear Algebra Textbooks“So far we have defined a mathematical system
called a real vector space and noted some of its properties ....
[In what follows], we show that each vector space V studied here has a set composed of a finite number of vectors that completely describe V. It should be noted that, in general, there is more than one such set describing V. We now turn to a formulation of these ideas.”
Following this, the text defines the concepts:Linear independenceSpanBasis
And rigorously prove all related theorems.
From a chapter on eigen theory“In this section we consider the problem of factoring
an n×n matrix A into a product of the form XDX-1, where D is diagonal. We will give necessary and sufficient condition for the existence of such a factorization and look at a number of examples. We begin by showing that eigenvectors belonging to distinct eigenvalues are linearly independent.”
Necessitating the Concept of Diagonalization
Logical Justification and Intellectual Need
Grassmann’s theory of extension (1844, 1862)
Grassmann’s idea of a sound foundation for mathematics designed to support both the method of discovery and the method of proof.
Grassmann’s [approach] appears to be much more than a device to aid the reader; he appears to regard the pedagogical involvement as an essential part of the justification of mathematics as science.
(Lewis, 2004, p. 17: History and Philosophy of Logic, 25, 15-36)