# Montreal 20001 The Theoretical Dimension of Mathematics: a Challenge for Didacticians Mariolina Bartolini Bussi Dipartimento di Matematica Modena - Italia.

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Montreal 20001 The Theoretical Dimension of Mathematics: a Challenge for Didacticians Mariolina Bartolini Bussi Dipartimento di Matematica Modena - Italia bartolini@unimo.it Plenary speech given at the 24th Annual Meeting of the Canadian Mathematics Education Study Group Université du Québec à Montréal - May 28th 2000

Montreal 20002 Theoretical knowledge PME reports forum 97 plen. 2000 4 teams Genoa (Boero) Modena (Bartolini) Pisa (Mariotti) Turin (Arzarello) All grades Complementary 2nd order approaches Epistemological Didactical Cognitive

Montreal 20003 Theoretical knowledge Book Kluwer to appear 4 teams All grades Complementary 2nd order approaches Epistemological Didactical Cognitive

Montreal 20004 Theoretical knowledge Semiotic Mediation From empirical to theoretical compass 5th grade Overcoming conceptual mistakes 7th grade

Montreal 20005 From empirical to theoretical compass (5th grade) Field of experience The functioning of gears in everyday objects: predictive hypotheses interpretative hypotheses

Montreal 20006 From empirical to theoretical compass (5th grade) Field of experience The functioning of gears in everyday objects: predictive hypotheses interpretative hypotheses

Montreal 20007 Algebraic and geometrical modelling T T TERC MA

Montreal 20008 The Task (5th grade) Draw a circle, with radius 4 cm, tangent to both circles. Explain carefully your method and justify it.

Montreal 20009 Veronicas solution The first thing I have done was to find the centre of the wheel C; I have made by trial and error, in fact I have immediately found the distance between the wheel B and C. Then I have found the distance between A and C and I have given the right 'inclination' to the two segments, so that the radius of C measured 4cm in all the cases. Then I have traced the circle.

Montreal 200010 Veronicas solution JUSTIFICATION I am sure that my method works because it agrees with the three theories we have found : The points of tangency H and G are aligned with ST and TR ; II) The segments ST and TR meet the points of tangency H and G ; III) the segments ST and TR are equal to the sum of the radii SG and GT, TH and HR.

Montreal 200011 The classroom discussion of Veronicas protocol Teacher : Veronica has tried to give the right inclination. Which segments is she speaking of ? Many of you open the compass 4 cm. Does Veronica use the segment of 4 cm? What does she say she is using ? [Veronica's text is read again.It becomes clear that she is using segments of 6 and 7 cms]

Montreal 200012 The classroom discussion Jessica : She uses the two segments... Maddalena :.. given by the sum of radii [Some pupils point with thumb-index at the sum segments on Veronica's drawing and try to 'move' them like sticks. They continue to rotate them till the end of the discussion]

Montreal 200013 The classroom discussion Teacher : How did she make ? Giuseppe : She has rotated a segment. Veronica : Had I used one segment only, I could have used the compass […]. I planned to make RT perpendicular and then I moved ST and RT until they touched each other and the radius of C was 4 cm.

Montreal 200014 The classroom discussion Alessio : I had planned to take two compasses, to open them 7 and 6 and to look whether they found the centre. But I could not use two compasses. Stefania P. : Like me ; I too had two compasses in the mind.

Montreal 200015 The classroom discussion Elisabetta [excited] : She has taken the two segments of 6 and 7, has kept the centre still and has rotated : ah I have understood ! Stefania P. :... to find the centre of the wheel... Elisabetta :... after having found the two segments... Stefania P. :... she has moved the two segments.

Montreal 200016 The classroom discussion Teacher : Moved ? Is moved a right word ? Voices : Rotated.. as if she had the compass. Alessio : Had she translated them, she had moved the centre. Andrea : I have understood, teacher, I have understood really, look at me … Voices : Yes, the centre comes out there, it's true. Moved? Rotated! Translated?

Montreal 200017 The classroom discussion Alessio : It's true but you cannot use two compasses Veronica : You can use a compass first on one side and then on the other. Teacher: Good pupils. Now draw the two circles on your sheet. [All the pupils draw the two circles on their sheet and identify the two solutions].

Montreal 200018 The two solutions

Montreal 200019 Veronicas first solution Dynamic / Procedural A circle is the figure described when a straight line, always remaining in one plane, moves about one extremity as a fixed point until it returns to its first position (Hero)

Montreal 200020 The final shared solution Static / Relational A circle is a plane figure contained by one line such that all the straight lines falling upon it from one point among those lying within the figure are equal to one another (Euclid)

Montreal 200021 An old (yet topical) problem ….

Montreal 200022 … for students Excerpt from an interview 11th grade I have already proved that that segment [KM] is always constant. … No, I haven't proved it because I haven't proved that this one [KM] rotates...or something like that.… Now I must also say why the locus is a circle, shouldnt I? Shall I prove it? After having proved that while C moves on C1, the segment KM (M is the midpoint of EF) does not change

Montreal 200023 INT. Haven't you done it? you said that this one [KM] always remains constant. It remains constant.... INT. How do you define a circle? I define it as locus.. you are right... locus of points equidistant from the centre... it crossed my mind that I had to prove also... no... maybe it is stupid... that I had to prove that it was rotating around the centre … from Mariotti, Mogetta & Maracci, 2000

Montreal 200024 … and for mathematicians The compass and the continuum Do the two circles surely meet? WHY?

Montreal 200025 Different answers The compass and the continuum EUCLID: Look at the lines in the drawing HERO: Rotate the two lines (sticks, fingers, arms …) until they clash DEDEKIND: If in a given plane a circle C has one point X inside and one point Y outside another circle C, the two circles intersect in two points (continuity).

Montreal 200026 In the experiment the compass is used To draw round shapes But also... V. Kandinsky

Montreal 200027 … the compass is evoked in the mind and simulated by means of gestures To draw circlesand to find points at a given distance

Montreal 200028 Semiotic Mediation The simple stimulus-response process is replaced by a complex, mediated act, which we picture as S --------------- R X [This auxiliary stimulus] transfers the psychological operation to higher and qualitatively new forms and permits humans, by the aid of extrinsic stimuli, to control their behaviour from the outside. The use of signs […] creates new forms of a culturally based psychological process (Vygotskij).

Montreal 200029 The enriched compass may be a tool of semiotic mediation drawing devices were used for centuries to construct and prove the existence of the solutions of geometrical problems of algebraic equations Cavalieris instrument for parabola

Montreal 200030 Our intuition about the continuum is built from invariants which emerge from a plurality of acts of experience: Time, Movement, The Pencil on a sheet Trajectories ……. Lacte de prévoir, anticiper une trajectoire constitue le fondement antique, lembryon pré- humain de labstraction géométrique humaine Giuseppe Longo, 1997 http://www.dmi.ens.fr/users/longo/geocogni.html

Montreal 200031 First Example The compass (and other drawing instruments) and the problem of continuum

Montreal 200032 Second Example The Abacus and the polynomial representation of numbers

Montreal 200033 Third Example The Perspectographs and the roots of projective geometry

Montreal 200034 Semiotic mediation Concrete artefacts Embodied cognition Concrete artefacts only?

Montreal 200035 Further examples: microwolds Geometry as a theory (Mariotti - Handbook - LEA - to appear) Algebra as a theory (Cerulli - to be presented in ITS 2000 Montreal - June)

Montreal 200036 Overcoming conceptual mistakes (5/7th grade) from Platos Meno: doubling the square

Montreal 200037 The teaching experiment the students Solve individually the problem posed by Socrates to the slave. Read Platos dialogue and detect, with the teachers guide, the three phases. Discuss the content and the different roles played by Socrates and by the slave, with the teachers guide.

Montreal 200038 Scheme of Platos dialogue The problem: doubling a square 1 The slave is self confident Socrates asks questions The mistake is detected by visual evidence

Montreal 200039 Scheme of Platos dialogue Towards the awareness that … 2 The slave is insecure Socrates asks questions and makes comments A new attempt

Montreal 200040 Scheme of Platos dialogue Towards a general solution 3 Socrates guides the slave with suitable questions The slave follows Socrates with suitable answers

Montreal 200041 The teaching experiment the students Choose another conceptual mistake in a different area, well known by the students Discuss collectively about the chosen mistake, with the teachers guide. Construct individually a Socratic dialogue about the chosen mistake Compare in collective discussion some dialogues produced by the students

Montreal 200042 The Task (7th grade) Write a Socratic dialogue about the following conceptual mistake By dividing an integer number by another number, one always gets a number smaller than the dividend

Montreal 200043 A closer look at the two examples CompassDialogue Aim To realise productive classroom activities about the theoreticalthe overcoming natureof shared of a physical conceptual instrumentmistakes

Montreal 200044 A closer look at the two examples CompassDialogue Task To produce a methoda dialogue of constructionaccording and itsto Platos justificationmodel

Montreal 200045 A closer look at the two examples CompassDialogue Instrumental use To use the compassPlatos dialogue to learn how to find points a square at a given with a double distancearea

Montreal 200046 The instrumental use of the compass

Montreal 200047 A closer look at the two examples CompassDialogue Mediational use To internalize the activitythe model with the physicalof Socratic compassdialogue to control ones own behaviour

Montreal 200048 A closer look at the two examples CompassDialogue Mediation takes place when? In the collective discussion AFTERBEFORE the individual task with the teachers guide

Montreal 200049 A closer look at the two examples CompassDialogue Mediation takes place how? With an essential role played by IMITATION of gesturesof genre of wordsof structure started, encouraged and explicitly required by the teacher

Montreal 200050 Nec manus nuda nec intellectus sibi permissus multum valet: instruments et auxiliis res perficitur (Bacon: The New Organon …, 1690 quoted by Vygotskij and Lurija, 1930) Neither the naked hand nor the understanding left to itself can effect much: it is by instruments and aids that the work is done Rembrandt

Montreal 200051 A question for the Working Group D Dynamic geometry Pointwise generation of loci Continuous generation of curves ANIMATION Which epistemological analysis?

Montreal 200052 A question for the Working Group A Which kind of mathematics preparation for primary school teachers if the aim is the approach to theoretical knowledge?

Montreal 200053 A question for the Working Group C Is the task of producing the Socratic dialogue a problem that may (must) be solved by division?

Montreal 200054 A question for everybody Have you ever tried to (re)construct a Socratic dialogue about a conceptual mistake of yours? Try and become teachers of yourselves!

Montreal 200055 A remind of some references on this collective project PME reports from 1993 first author: Arzarello, Bartolini, Boero, Garuti, Mariotti (et al.) Mariotti et al., forum, PME 1997 (Lahti). Arzarello, plenary, PME 2000 (Hiroshima). Some other conferences Bartolini, plenary, ICM98, Berlin, 1998 Mariotti, Mogetta & Maracci, NCTM presession, Chicago, 2000 Cerulli & Mariotti, Montreal, ITS 2000 (June) International Journals and volumes Bartolini, ESM 96 Bartolini et al. ESM 99 Bartolini & Mariotti FLM 99 Mariotti, in English et al. (ed.), Handbook …, LEA (to appear) Book Boero (ed.), Theorems in school, …, Kluwer, to appear

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