The greatest enemy of unity, or even just some kind of organisation in psychology, is complacency. Hayes (2004) argues that Henriques' attempt to (re)define psychology is essentially redundant as it won't result in any practical benefits. Hayes points to how his own house (behaviour analysis) is apparently in good theoretical order and has no need of these over-arching meta-theories. Further he wants to say that there is no way of knowing what benefits will accrue from developing a unified view of psychology - apparently coherence has no proven benefit.

Coherence has no proven benefit?

Since there is no way to conceive of the exact benefits of a theory we don't yet have, the only argument available is by analogy to theoretical unity in other disciplines. Does a unified theory of the fundamental forces of nature have any proven benefit? The physicists seem to think so. Has Darwin's theory been beneficial? Biologists seem to think so, along with others from many differen disciplines.

Surely only the most complacent of psychologists could deny the possible benefits of unification. Many are keeping their heads down and working within a paradigm that appears internally consistent. It's time to look up and see what everyone else is doing.

Hayes (2004) Taxonomy as a Contextualist Views It (Abstract)
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