The first thing psychology students learn about intelligence is that Boring's (1923) definition of intelligence as what an IQ-test measures is just silly. But this article says there is a reason to reconsider this opinion on this topic. The core of intelligence tests rests on positive manifold: the fact that all intelligence subtests correlate positively. The factor model is a reflective latent variable model, in which the factor is a hypothesized entity that is posited to provide a putative explanation for the positive manifold. The principal component is a formative model, in which the components are conveniently weighted total scores. So, the factor model embodies the idea that there is a common cause 'out there' that we 'detect' using the factor analysis.
The classical g model (Jensen) is a reflective model: whatever g is, it is thought to explain scores on tests, correlation between tests, and individual differences between subjects or groups of subjects. So, the g-factor is seen as the common cause of the correlation in the positive manifold.
Lately, there has also been an alternative explanation for the positive manifold that has been proposed in the form of the mutualism model. In this model, the correlations between the test scors are not explained through the dependence on a common latent variable, but as a result of reciprocal positive interactions between abilities and processes that play a key role in cognitive development, such as memory, spatial abiilty and language skills. But, the mutualism model explains the positive manifold but at the same time denies the existence of a realistic g. So, it motivates the formative interpretation of the factor analytic model. But, if this is true, than the search for a 'g' would be fruitless.
One crucial difference between the reflective and formative models concerns the role of the indicator variables. In a reflective model are these indicators exchangeable. Therefore, different working memory tests, with different factor loadings could be added to a test battery without changing the nature of the measured g factor. In a formative model are the indicators not exchangeable, unless they are completely equivalent. Also, in a formative interpretation of IQ test scores there really is no such thing as a seperate latent variable that we could honour with the term 'intelligence' and it is questionable whether one should in fact use the word 'intelligence measurement' at all situations.
