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Intelligence ………………………..(to prove) surprisingly difficult to define in a rigorous
fashion. Clearly it refers in a general fashion to the level of ability to reason, solve problems, successfully respond to situations and so forth, but these range from mathematics to handling social situations, from understanding machines to solving crosswords and Sudoku puzzles. Psychologists such as Francis Galton (using the expression 'natural ability') and the American Raymond B. Cattell ……………………..(to begin) attempting to study intelligence in the late nineteenth century, this culminating in the pioneering statistical studies of C. Spearman and, most famously, Alfred Binet and H. Simon in France who …………………………..(to produce) the first intelligence test in 1904, to which all subsequent IQ (intelligence quotient) tests trace their origins. These all ………………………..(to focus) primarily on reasoning ability and academic performance, ignoring social intelligence and emotional intelligence. One should stress here that it was the advent of universal education which …………………………(to create) the climate in which an assessment scale applicable to all children was required, IQ tests being Psychologys response to this. Throughout the twentieth century, IQ testing and theories of intelligence …………………………(to enjoy) a chequered and controversial history. IQ testing itself ………………………….(to evolve) quite rapidly after Binet and Simon's work. Initially IQ …………………………..(to define) as the ratio between mental age (MA) and chronological age (MCA) but it was obvious from the outset that this was inapplicable to people much over 15 years old and so was replaced by a statistical definition in terms of standard deviations from population norms. The term IQ itself ………………………..(to introduce) by the German psychologist Wilhelm Stern who converted the MA:CA ratio into a simple quantitative scale,defining MA = CA as 100. The definition of mean intelligence as 100 ……………………(to continue) ever since.
(from Graham Richards “Psychology. The Key Concepts”)

Intelligence proves surprisingly difficult to define in a rigorous fashion. Clearly it refers in a general fashion to the level of ability to reason, solve problems, successfully respond to situations and so forth, but these range from mathematics to handling social situations, from understanding machines to solving crosswords and Sudoku puzzles. Psychologists such as Francis Galton (using the expression 'natural ability') and the American Raymond B. Cattell began attempting to study intelligence in the late nineteenth century, this culminating in the pioneering statistical studies of C. Spearman and, most famously, Alfred Binet and H. Simon in France who produced the first intelligence test in 1904, to which all subsequent IQ (intelligence quotient) tests trace their origins. These all focused primarily on reasoning ability and academic performance, ignoring social intelligence and emotional intelligence.

One should stress here that it was the advent of universal education which created the climate in which an assessment scale applicable to all children was required, IQ tests being Psychology's response to this.

Throughout the twentieth century, IQ testing and theories of intelligence enjoyed a chequered and controversial history. IQ testing itself evolved quite rapidly after Binet and Simon's work. Initially, IQ was defined as the ratio between mental age (MA) and chronological age (CA) but it was obvious from the outset that this was inapplicable to people much over 15 years old and so was replaced by a statistical definition in terms of standard deviations from population norms. The term IQ itself was introduced by the German psychologist Wilhelm Stern who converted the MA:CA ratio into a simple quantitative scale, defining MA = CA as 100. The definition of mean intelligence as 100 has continued ever since.

(Translation: The passage discusses the difficulty in defining intelligence and its different aspects. It mentions that psychologists began studying intelligence in the late nineteenth century and developed intelligence tests, which primarily focused on reasoning ability and academic performance. These tests were a response to the need for a universally applicable assessment scale due to the advent of universal education. IQ testing and theories of intelligence have had a controversial history, with IQ tests evolving over time to use statistical definitions. The term "IQ" was introduced by Wilhelm Stern, who defined it as a ratio between mental age and chronological age. This definition has remained unchanged.)