As per my shallow research, IR literature and online content intermix Scientific and Behavioral Approach to International Relations. What exactly is the difference between the Scientific and Behavioral approach to International Relations? Elaboration will be highly appreciated.
The Behavioral Revolution and International Relations provides a broad overview of both rational and behavioural approaches to international relations, beginning with the recent conflict between the U.S. and Iraq as the preface by which different approaches to international relations analyze the strategies involved on either side at different points in time
What explains the strategically costly and ill-planned American invasion and occupation of Iraq? What accounts for Saddam Hussein's failure to take actions that might have deflected it? These decisions can be explored with rationalist tools, including the existence of credible commitment problems and asymmetries in information. 1 But explanations of this sort beg a number of important questions. The Clinton and Bush administrations did not differ substantially in their information about Iraq. But Bush administration officials—and the president himself—did hold beliefs that differed substantially from those of their predecessors, and those beliefs had profound effects.
Decision making by both Iraqi and US leaders displayed strong biases. Saddam Hussein failed to recognize that the United States was committed to war unless he was willing to reveal credibly that he had, in fact, dismantled his weapons of mass destruction. The United States signaled its intentions repeatedly, but the Iraqi leader remained impervious to new information. Bush administration officials believed that the Americans would be greeted as liberators and democracy would flourish of its own accord. Such motivated reasoning both precipitated war and contributed to the failure to plan adequately for rebuilding the Iraqi state in war's wake. The causes of the Iraq War and the disastrous consequences of its aftermath appear to lie as much in the realm of beliefs and decision making as in standard theories of bargaining.
From an analytical perspective, the rational model assesses practical realities and from the expected outcomes of various potential decisions, selects the prospective decision that the primary actors will make. For example, if the geography of a region is rich in mineral or metal resources, it is rational to anticipate mining to occur. The resources are there, actors will attempt to control those resources and make the most possible profit from the enterprise. War could ensue over various entities vying for dominance of the geographic region which contains natural resource deposits.
The behavioural approach would tend to not simply base the assessment on the rational and practical tendency to extract minerals and metals from the geography; instead, experimental models using humans as actors would simulate what decisions the actors might make regarding the natural resource deposits. That is, if the geography is historically significant to the populace, intensified mining could be halted or reduced by the primary actors to preserve the cultural significance of the region, instead of employing the rational choice of extracting as much resources as possible from the geography, irrespective of behavioural implications, those behavioural nuances could be primary factors in assessing long-term policy decisions that might appear to be contrary to the scientific approach of harvesting as much resources and acquiring as much political power as is possible in the least amount of time.
There is no bright line for the strategist mandating that they adhere to one of the particular models, or either of them; or not both simultaneously. The requirement is to achieve strategic advantage for the principal; irrespective of the academic labels applied to the means employed to do so.
In political science, behavioralism was a theory which attempted to bring a more scientific approach to the field. In a lot of ways, their work was an attempt to subject political science to the kinds of methods used in the natural sciences.
Much of this information is based on my graduate seminars, where we talked about the history and development of the discipline. I'll add references where I can, but if you feel like something needs more support just say so and I'll try to dig it up.
Early Political Science
Early political science was not very scientific. The discipline was organized around the time of World War I. Many early political scientists were diplomats, government officials, and lawyers with expertise in comparative or international law. They had normative goals of ensuring international stability.
Around the 1930s there was strong movement to make political science scientific.Their notion of 'scientific' was an approach that was based on quantitative hypothesis-testing. The predominant theory of this time was behavioralism which focused on the behavior of individuals.
One example is the 'Easton model' (also referred to under the broader names of systems theory or cybernetic theory). Easton proposed that the policy environment could be understood at the "inputs" to a person and observing the output. There is feedback in this relationship because the person's decisions influence the inputs for other decisions.
(Image from the University of Hawaii)