introspection produced subjective data therefore hard to establish general laws
Watson and B.F Skinner proposed that behaviours should only be studied if observed objectively and measured
behaviourists focussed on behaviours they could see and used controlled experiments
1950's cognitive approach
digital revolution allows psychologists to link mind to computer e.g multi-store model and tested predictions using experiments
1980's biological approach
advances into technology allowed for more research into physiological processed as they happen e.g fMRI and EEG for brain scanning and genetic testing
Strength
modern psychology can claim to be scientific - psychology has same aims as natural science. learning, cognitive, biological approaches all use scientific techniques to test claims, suggests that throughout 20th century psychology has established itself as a science
Limitation
not all approaches use objective methods - humanistic approach rejects scientific approach focussing on individual/subjective experience, psychodynamic approach used case studies which don't have representative samples, any human ps in a study may fall into demandcharacteristics, therefore scientific approach to study human thought may not always be desirable/possible