Gardner's theory of multiple intelligences is indeed theory?

Theory should explain something, provide evidence and make predictions. That doesn’t mean that a theory is indisputable. A theory can be proved wrong or added upon.

So let’s see reliability and validity of Gardner’s theory. Maybe you assume that the theory became popular based on supportive study results. The truth is that the first study to test the theory was published 23 years after the theory was made public. The study did not support Gardner’s theory of multiple intelligences.

Until now the theory is not empirically validated. It is very difficult to measure the different types of intelligence and some of them is even hard to be defined. So, if we are not sure what these “intelligences” are or how to assess them, then we can not talk about a theory.

Furnham (2009) examined a self-report measure of multiple intelligences and its pattern of correlations with a measure of the five-factor model of personality traits (openness to experience, conscientiousness, extraversion-introversion, agreeableness, neuroticism). The findings shows high intercorrelation with each other. Moreover, there were many correlations between the eight intelligences and the five-factor model. These results are in opposition to the theory that all the “intelligences” are supposed to represent distinct and not related domains.

I understand that this theory may seem nice and convenient. Everybody is smart but in different sectors. Rationally thinking, if everyone is intelligent, then no one is. Of course, we could approach this topic from philosophical view and not try to examine if it is true or false, according to scientific data. In every case, the word “theory” is referred to something specific and is at least a linguistic false.