American Philosophical Society
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1Name:  Dr. Philip N. Johnson-Laird
 Institution:  Princeton University
 Year Elected:  2006
 Class:  3. Social Sciences
 Subdivision:  305
 Residency:  Resident
 Living? :   Living
 Birth Date:  1936
   
 
Philip N. Johnson-Laird was born in Yorkshire, England, in 1936. He left school at the age of 15 and spent ten years in a variety of occupations until he went to University College, London to read psychology. He later gained his Ph.D. there under the supervision of Peter Wason, and he joined the faculty in 1966. In 1971, he was a visiting member of the Institute of Advanced Study, Princeton, where he began a collaboration with George A. Miller. Subsequently, he held positions at the University of Sussex (1973-1981) and at the Medical Research Council's Applied Psychology Unit (1981-1989) in Cambridge, where he was also a Fellow of Darwin College. He returned to Princeton in 1989 to be a member of the faculty at the University, where he is the Stuart Professor of Psychology. He has published 12 books and nearly 300 scientific articles. He has received the Spearman medal and the President's award of the British Psychology Society as well as six honorary degrees. He is a fellow of the Royal Society and the British Academy. He is married to Maureen Johnson-Laird (née Sullivan) and has two grown-up children. In his spare time, if he had any, he would compose music and play modern jazz piano. Research: Dr. Johnson-Laird's study of the psychology of reasoning began in a collaboration with Peter Wason. They discovered that people make systematic and predictable errors in reasoning, and that they are affected by the content of inferences (see their joint publications 1969-1973, his study with Paolo and Maria Sonino Legrenzi, and the book, Psychology of Reasoning, 1972). Effects of content are embarrassment to the thesis that there is a mental logic consisting of formal rules of inference. During the 1970s, his research also concerned psycholinguistics, and the representation of meaning and discourse (see, e.g., Miller and Johnson-Laird, Language and Perception, 1976). Later, he proposed that individuals reason, not from the logical form of assertions, but from their representation of discourse in the form of mental models. Each mental model represents a different possibility. The fundamental principle of human rationality is accordingly that an inference is valid if it has no counterexamples, i.e., models of possibilities in which the premises are true but the conclusion false. His experiments corroborated the prediction that the greater the number of models of possibilities, the longer inferences take and the more likely reasoners are to make errors. He also began the development of a series of computer programs implementing the model theory. This research led to the publication of his book, Mental Models, in 1983, which integrated the theory of discourse representation and the theory of human reasoning. One gap in the theory concerned reasoning based on sentential connectives, such as "if" and "or". In research at the MRC Applied Psychology Unit in Cambridge, Ruth Byrne and Johnson-Laird showed how to extend the theory to such inferences, implemented it in a computer program, and carried out a series of experiments corroborating the theory (see their book, Deduction, published in 1991). The computer program also solved a well-known problem in logic: the search for a maximally parsimonious circuit equivalent to a given circuit made up from Boolean units. In simple cases, naïve reasoners tend to draw the corresponding conclusions from premises containing sentential connectives. Since his move to Princeton, Dr. Johnson-Laird and his colleagues have extended the model theory to a number of novel domains, including temporal reasoning, causal reasoning, modal reasoning about what is possible and what is necessary, deontic reasoning about what is permissible and obligatory, and reasoning based on diagrams. This research has been carried out with many colleagues in different countries: Belgium, Canada, France, Germany, Ireland, Italy, Portugal, Spain, the UK, and the USA. He has also developed a theory of emotions with his colleague Keith Oatley at the University of Toronto. This theory postulates that emotions serve a quasi-rational function, enabling social mammals including primates to make adaptive responses to their social environment without the need for complex cognition. Johnson-Laird's main recent discovery is of a psychological principle that severely constrains human rationality: individuals normally represent what is true, but do not represent what is false (the principle of truth). In this way, they try to overcome the bottleneck of working memory, which has a limited processing capacity. To represent only what is true appears to be sensible, but, as a computer program revealed, inferences exist where the principle leads reasoners astray. His series of recent studies have shown that highly intelligent adults readily succumb to these so-called "illusory" inferences (see, e.g., the publication in Science, 2000, with his colleagues, Vittorio Girotto, and Paolo and Maria Legrenzi). Although the illusory problem are sparse in the set of all possible inferences, the illusions take many forms. One compelling instance arises from premises of the following sort: If my hand contains a king then it contains an ace, or else if it doesn't contain a king then it contains an ace. My hand does contain a king. What follows? The obvious conclusion is that my hand contains an ace. But the inference is fallacious, because the force of "or else" is that one of the conditionals at the very least may be false. In his most recent research, Johnson-Laird is examining the regions of the brain underlying deductive reasoning using functional magnetic resonance imaging. He and his colleagues have shown that deduction activates right hemisphere, and that a search for counterexamples appears to depend on the right frontal pole. A separate series of brain -imaging studies has corroborated his behavioral findings that materials that evoke visual imagery impede reasoning (see his study in Memory & Language, 2002, with Markus Knauff).
 
Election Year
2006 (1)