Context: Metaphysics of perception explores fundamental questions regarding the structure and status of the perceived world (or the world qua perceived. As such, it must not be separated from metaphysics per se. Problem: Although philosophy should be distinguished from the history of philosophy, it is nevertheless, say, sensitive to history. It means that in doing philosophy in general and metaphysics in particular, we re-establish, re-think ideas - questions and answers - of our antecessors; we set them anew so that they are vivid roots of contemporary thinking. My point is that movements in contemporary philosophy and cognitive science, such as radical constructivism or enactive and embodied cognition, need a metaphysical grounding. Method: I present a more elaborate account of PL-metaphysics as proposed by Jerzy Perzanowski, i.e., the stream of ideas grounded first of all in the conceptions of Plato and Leibniz. PL-metaphysics shall be compared to what I call, in the same spirit, DL-metaphysics, i.e., the stream grounded in the ideas of Descartes and Locke. On this basis, I propose to reconsider radical constructivism and pursue the question whether PL-metaphysics has anything interesting to offer in this field. Results: PL-metaphysics does have something interesting to offer due to the fact that according to it, perception is not conceived of as a transmission from an “objective” reality to the internal mental realm; as a result of perception, reality is actualized in some way, i.e., it acquires some presentation(s) or appearance(s. By virtue of perception, the apparent world comes to existence. This, however, does not mean that the apparent world is a projection of mind, that it exists “in the head.” Implications: PL-metaphysics reconciles realism with constructivism. As such, it might be considered either an alternative to constructivism or an improvement and completion of this position. Constructivist content: The article refers to non-Cartesian movements in contemporary philosophy, including radical constructivism, enactive and embodied cognition. Keywords: Perception, metaphysics, radical constructivism, realism, appearance, Jerzy Perzanowski, Plato, Gottfried Willhelm Leibniz, Ernst von Glasersfeld.

Constructivist approaches are met with growing interest in the field of psychology In this paper, three variants of constructivism will be dealt with (1) the individual-centred constructivism of the theory of personal constructs proposed by George Kelly, (2) radical constructivism in the sense of Ernst von Glasersfeld and Heinz von Foerster, and (3) social constructionism as represented by Ken Gergen This paper outlines the theory of personal constructs as the first subject-theoretical and constructivist approach in psychology, considers the reasons for the rather ambiguous reception of radical constructivism in psychology, and explains why social constructionism can be seen as the most promising variant of constructivism today by presenting two examples the social construction of psychological disorders and the social construction of creativity The central question about the empirical content of psychological theories is answered from a social-constructionist point of view The conclusion is that empirical research in psychology remains possible and useful Finally, recent critical comments concerning the extension of social constructionism to the natural sciences are briefly discussed.

Open peer commentary on the article “Examining the Role of Re-Presentation in Mathematical Problem Solving: An Application of Ernst von Glasersfeld’s Conceptual Analysis” by Victor V. Cifarelli & Volkan Sevim. Upshot: In this commentary, I address the viability of conducting constructivist teaching experiments to develop models of students’ conceptualizations. I also discuss how this research tradition has been adapted by researchers to conduct classroom teaching experiments. In my concluding remarks, I address the need for researchers to develop models for teacher learning.

This article reports part of a study (Wright 1989b, 1990c, 1988) in which the epistemology of radical constructivism (e.g., von Glasersfeld 1987, in press) was used as a basis for a teaching experiment which involved an investigation of the mathematics learning of young children. The research methodology adopted for the study has been expounded by Cobb and Steffe (e.g. Cobb & Steffe 1983; Steffe & Cobb 1988) and, according to Sinclair, is “methodologically… original, … [and] longitudinal but not naturalistic” (1988: v). Further, the methodology is hermeneutic rather than positivistic (Candy 1989: 2–3), has much in common with phenomenographic approaches (e.g., Marton 1981, 1987; Neuman 1987) and, as Hockings advocates when describing insights for educational researchers from the science of chaos, “has [moved] away from a reductionist approach to knowledge and [works] across discipline boundaries” (1990: 17). The article begins by briefly reviewing recent developments in K-6 mathematics in order to demonstrate, in general terms, the compelling need for research into mathematics learning.

Key words: teaching experiment, teaching session, number word, radical constructivism, counting type.