The diagnostic process is a crucial aspect of medical practice. Psychiatric diagnosis involves information gathering, mental state assessment, hypothesis integration with laboratory or imaging when needed, and data interpretation. Clinical reasoning operates through two systems: System 1, characterized by intuitive pattern recognition; and System 2, which employs meticulous critical thinking. These systems complement each other, with System 1 being faster but riskier while System 2 offers a more planned approach. Today, the Diagnostic and Statistical Manual of Mental Disorders (DSM) and the International Classification of Diseases (ICD) are the two primary diagnostic manuals. Despite their imperfections and reliance on symptom descriptions, the DSM and ICD remain indispensable tools in psychiatry for communication, research, and clinical decision-making.

While psychiatry has made great strides in recent decades toward integrating our increasing understanding of the biological bases of cognition, it nonetheless continues to suffer from imprecise diagnostics and blunt treatment options. Recent advances in computational neuroscience have the potential to address these issues, with a range of neural and cognitive models offering the possibility of a more precise psychiatric nosology with more targeted therapeutics. Here we review a variety of these models, with a special emphasis on their application to addiction, psychosis, anxiety disorders, depression, obsessive-compulsive disorder, autism spectrum disorder, and attention-deficit hyperactivity disorder. We then close with a discussion of potential challenges in incorporating these insights and methods into a clinical setting.

The causal-reductionist model has resulted in a classification system and set of treatments for mental health that assumes people are self-contained individuals, operating independent of context. Despite the good efforts of community psychology and a number of progressive therapists, as well as the historic meaage of the anti-psychiatry movement, the powerful role of social class and particularly poverty on mental health is disregarded. This is epitomized by the positive psychology movement, the focus on individual happiness (independent of context), and the development of a 'happiness index' which regards progress as being independent of GDP and other material measures. In essence, 'positive thinking' and 'be happy psychology' is proposed as a solution. But even positive psychologists have been forced to admit that the probablity of mental health problems increases as we move down the social classes, so that poverty is a powerful context leading to a higher probability of individuals suffering mental health problems.

Concerns that American psychiatry was neglecting an important dimension of human experience led to the introduction into DSM-IV of a V Code for a Religious or Spiritual Problem. The 1994 DSM-IV also included the new Outline for a Cultural Formulation, later accompanied by a Cultural Formulation Interview and 12 Supplemental Modules added to help clinicians to gather information for the Outline for Cultural Formulation. Recommendations from the APIRE Workgroup led to revisions in DSM-5, and outlined several areas for future research into the implications of spirituality, religion and culture for diagnosis and treatment. In particular, future research will need to better clarify the relationship between spiritual/religious and psychopathological phenomena, the different manifestations of psychiatric disorders in religious populations, the influences of spirituality/religion on the course and outcome of mental disorders, and the role of spirituality/religion in developmental and personality disorders.

We examine why science is important to applied psychology, even if one’s motivation to be a psychologist is primarily practical. Helping others takes knowledge and skill, and often applied psychologists face situations that do not produce immediate or clear outcomes. In such situations experiential learning can only do so much, and science is needed to be effective long term. When the history of training models in applied psychology is reviewed from the inception of the field to the present day, it is clear that students of applied psychology need to learn how to do research that will inform practice, how to assimilate the research evidence as it emerges, and how to incorporate empiricism into practice itself. We argue that the kind of knowledge needed by practitioners requires a focus on the needs of those served by psychologists, a more personalized and process-based research approach, and a laser-like focus on issues of broad importance. A scientist-practitioner is a consumer of research, but is also able to identify, acquire, develop, and apply empirically supported treatments and assessments to those in need, and to think about their own work with an empirical mind set.

In a commentary on Miller and Bartholomew, Zachar notes that the Research Domain Criteria initiative (RDoC) has always represented an incursion of cognitive neuroscience and factor analytic dimensional models from psychology into biological psychiatry, and that non-reductionist aspirations have been a part of RDoC from the beginning. Rather than reductionism, a more problematic tenet of the RDoC initiative is a contempt for the categories of the DSM, seen in a tendency to blame the lack of progress on adherence to a categorical model rather than on the intrinsic complexity of psychopathology.One aspect of this complexity is the open nature of psychological concepts.Turning to the “neural circuit” metaphor, Zachar suggests that the notion of a “circuit for” may reflect adopting too modular a theory of mind, which as a framework, may unnecessarily constrain a mechanistic science.

To define descriptive psychopathology as classification of disorders with respect to manifest signs and symptoms as opposed to deeper causes is a somewhat superficial construal that does not take into account the various ways that something can be brought under a description.The philosopher’s notion of bringing something under a description can be illustrated by a non-behaviorist reading of Gilbert Ryle’s book The Concept of Mind. That things can be brought under more than one description highlights the importance of re-describing. An important example of re-describing psychopathology is the discovery of panic disorder from which five desiderata for useful descriptions and re-descriptions can be derived. With respect to causes, the elucidation of a causal model for a phenotype can often lead us to notice something descriptively that we had not noticed before, in which case the causal model becomes part of a thicker description of the phenotype.

People often find statistics confusing because anecdotes more effectively tell stories and no one’s direct experience matches the statistical realities. The younger any individual is introduced to any drug the higher the risk of developing dependence. This is especially true for marijuana because it affects neurodevelopment in early adolescence. However, Horwood has shown than the lifetime rate of marijuana dependence does not accurately portray the overall progression of use because the majority of those who ever become dependent discontinue or reduce use sufficiently to no longer meet the DSM criteria for Cannabis Use Disorder (CUD). While 43% of those with onset of marijuana use at 13 years old meet criteria for CUD at some time by age 30, only 15% are dependent during the previous year at 30. The generally accepted rate of CUD for those 12 and older who have ever used marijuana is approximately 9%, compared to a 15% dependence rate for alcohol. The more frequently individuals use marijuana, the more they use on each occasion. The increased rates of marijuana use in Conduct Disorder (CD), Antisocial Personality Disorder (ASPD) and Attention Deficit Hyperactivity Disorder (jsADHD) are discussed.

As in many sciences, description is an important component of theory, research, and practical applications in clinical psychology. Despite this, considerable disagreement exists regarding how to describe the diverse manifestations of psychopathology that clinicians and researchers have observed. The disagreements are such that translating research across descriptive psychopathology models can be difficult or impossible, impeding scientific progress. As this chapter reviews, at least four major descriptive psychopathology approaches exist – clinical theory, descriptive psychiatry, quantitative models, and biological models – each of which has unique goals, units of observation, theoretical concepts, and research traditions. Through reviewing these dominant approaches, it is illustrated how diverging language, concepts, and methods can impede communication between scientists and practitioners working within different descriptive approaches. Beyond this, specific emerging descriptive psychopathology models (i.e., HiTOP, RDoC, and transdiagnostic processes) are reviewed, which have primarily developed as a response to descriptive psychiatry’s limitations (e.g., DSM) and may advance clinical psychology. Despite the promise of these emerging descriptive models, each is still primarily rooted in one traditional descriptive approach and retains that approach’s limitations. Thus, the chapter concludes by discussing the need to integrate descriptive psychopathology approaches and the challenges associated with this task.

In his chapter, Eric Turkheimer argues that psychiatric reduction is a doomed project because mental illnesses have properties that make them scientifically unruly; properties we might call, following the philosophical literature, “multiple realizability” and “social constructedness.” While it may be defensible to maintain that psychiatric syndromes are multiply realized social constructions, and thus not appropriate targets for reductive explanation, I argue that it is less obvious that all psychiatric entities share these properties. It may well be that reductionist projects will do better in psychiatry when they focus on explaining lower-level entities (for example, pathological mechanisms at the level of the cell or the neural circuit) that are only part of the puzzle of psychopathology. However, the promise of this sort of “patchy reductionism” needs to be evaluated in light of the ethical demands on psychiatric researchers not only to expand scientific knowledge but to improve clinical care and outcomes.