The main branches of science are commonly grouped into the natural sciences, social sciences and formal sciences, although classification systems vary between institutions and disciplines. Natural sciences investigate aspects of the physical and biological world and commonly include physics, chemistry, biology and Earth sciences. Social sciences investigate human behaviour, societies, institutions and relationships and include disciplines such as psychology, sociology, economics, political science, anthropology and human geography.
Formal sciences, including mathematics, statistics, logic and theoretical computer science, study abstract structures, relationships and systems using formal reasoning rather than empirical observation as their primary foundation. Some classification systems distinguish physical sciences from life sciences and Earth sciences, while others group disciplines according to methods or objects of study. Interdisciplinary fields such as environmental science, neuroscience, materials science, biochemistry and planetary science cross conventional boundaries and demonstrate that scientific knowledge does not always fit neatly into separate categories.
Physics is the science concerned with matter, energy, motion, forces, fields, space, time and their interactions. Classical physics includes mechanics, thermodynamics, electromagnetism and optics, while modern physics includes quantum mechanics, relativity, particle physics and condensed matter physics. Physics seeks mathematical descriptions of fundamental processes and often provides foundational principles used by other sciences. Chemistry focuses on matter, its composition, structure, properties and transformations. It examines atoms, molecules, chemical bonds, reactions, thermodynamics, kinetics and interactions among substances. Chemistry overlaps substantially with physics through physical chemistry and with biology through biochemistry. Together, physics and chemistry provide mechanisms relevant to materials, energy systems, biological processes, atmospheric chemistry and numerous technological applications.
Biology is the science of living organisms and includes molecular biology, genetics, cell biology, physiology, microbiology, ecology, evolutionary biology, zoology and botany. Modern biology operates across multiple scales, from molecular interactions and cellular processes to organisms, populations, communities and ecosystems. Evolutionary theory provides a central framework connecting many biological observations by explaining how inherited variation and differential reproductive success can produce changes in populations over generations. Earth sciences investigate Earth and its components, processes and history. Major Earth science disciplines include geology, geophysics, geochemistry, meteorology, oceanography, hydrology, glaciology and soil science. Earth scientists investigate processes such as plate tectonics, erosion, atmospheric circulation, ocean dynamics, earthquakes, volcanic activity and the cycling of water and materials.
Astronomy and planetary science investigate objects and processes beyond or throughout planetary systems. Astronomy includes the study of stars, galaxies, nebulae, black holes, planets and cosmic radiation, while planetary science examines planets, moons, asteroids, comets and planetary environments. Astrophysics applies physical principles to astronomical phenomena, making it a strong example of interdisciplinary science. Environmental science integrates biology, chemistry, Earth science, atmospheric science and other disciplines to study interactions among natural systems and human activities. Climate science similarly combines atmospheric physics, oceanography, geology, chemistry, ecology and computational modelling. Such fields illustrate why scientific branches are organisational categories rather than completely isolated bodies of knowledge. Complex real world problems frequently require concepts and methods from several disciplines simultaneously.
The social sciences apply systematic empirical and analytical methods to human behaviour and social organisation. Psychology studies behaviour and mental processes, sociology investigates social relationships and institutions, economics examines production, exchange, allocation and consumption of resources, political science studies political systems and behaviour, and anthropology investigates humans across cultural, biological and historical dimensions. Social science methods include experiments, surveys, interviews, observational studies, longitudinal research, statistical analysis, archival research and comparative studies. Human systems can be especially difficult to study because people respond to being observed, social contexts change and ethical constraints can limit experimental manipulation. These challenges affect research design but do not eliminate the possibility of systematic empirical investigation.
Formal sciences differ from empirical natural and social sciences because their primary objects are abstract systems rather than directly observed physical or social phenomena. Mathematics studies quantities, structures, patterns and relationships through formal deduction. Logic examines valid inference and formal systems. Statistics develops methods for describing data, quantifying uncertainty and drawing inferences from samples. Computer science includes both formal theoretical areas and empirical investigation of computational systems.
Formal methods can provide essential foundations for empirical science, including mathematical models, statistical tests and logical frameworks. However, a mathematical proof establishes that a conclusion follows from specified premises; it does not by itself establish that those premises accurately describe the physical world. Empirical validation is therefore required when mathematical models are used as representations of nature.
Interdisciplinary and applied sciences occupy important positions between traditional branches. Neuroscience combines biology, psychology, medicine, chemistry, physics and computer science to investigate nervous systems. Biochemistry studies chemical processes within living organisms. Geophysics applies physical principles to Earth, while geochemistry applies chemical principles to geological systems. Materials science combines chemistry, physics and engineering to understand and design materials. Epidemiology combines statistics, biology, medicine and social science to investigate patterns and causes of disease in populations. Data science integrates statistics, computing and domain knowledge to extract information from large datasets. These fields demonstrate that scientific classification is useful for organisation and education but does not establish rigid boundaries around knowledge.
There is no single universally mandatory list of the main branches of science because classifications serve different purposes. Educational systems may use broad categories such as physical science, life science and Earth science, while universities divide knowledge into departments containing much narrower specialties. Research agencies may classify disciplines according to funding categories, and libraries may use separate systems for organising publications. The important distinction is between scientific disciplines and the empirical principles they share.
Physics, chemistry, biology, Earth science and social science study different systems and use different specialised methods, but all can employ evidence, measurement, modelling, statistical reasoning and critical evaluation where appropriate. The boundaries between branches continually evolve as new fields develop, making scientific classification a practical organisational framework rather than a fixed natural division of knowledge.
