Natural science is the study of the physical world and everything in it, from atoms to ecosystems to galaxies. More formally, it covers any field that deals with matter, energy, and their interactions, or with phenomena that can be objectively measured and tested. If a discipline tries to understand something that exists in nature through observation and experimentation, it falls under the natural science umbrella.
The Main Branches
Natural science splits into two broad categories: life sciences and physical sciences. Within those, five primary branches cover the field.
Biology is the life science side. It encompasses everything alive, from single-celled organisms to complex ecosystems. Sub-fields include botany (plants), zoology (animals), microbiology (microscopic organisms), marine biology, genetics, molecular biology, and neuroscience, among dozens of others.
The physical sciences cover non-living systems and include four branches:
- Physics studies matter, energy, and how they interact, covering everything from the behavior of subatomic particles to the motion of planets.
- Chemistry focuses on the properties of substances and how they change when they react with one another.
- Earth sciences examine Earth itself, its atmosphere, oceans, and geology, including sub-fields like meteorology and geology.
- Space sciences (or astronomy) study everything beyond Earth: stars, planets, galaxies, and the structure of the universe.
These five branches aren’t sealed off from each other. Some of the most active fields in science today sit at the intersections: biochemistry bridges biology and chemistry, biophysics applies physics principles to living systems, and bioinformatics combines biology with computational methods. Synthetic biology and human brain science are other examples of fields that emerged where existing disciplines overlap.
How Natural Science Works
What makes natural science “science” rather than philosophy or opinion is its method. Every explanation must be grounded in events or mechanisms that can be observed in the natural world. The process follows a familiar loop: observe something, form a hypothesis to explain it, then gather evidence to test whether that hypothesis holds up. If the evidence contradicts the hypothesis, it gets rejected or refined. If it survives repeated testing by independent researchers, it gains acceptance.
A critical feature of this process is falsifiability. For a hypothesis to count as scientific, it has to be constructed so that it could, in principle, be proven wrong. A claim that can never be tested against real-world evidence falls outside the boundaries of science. A scientific “fact,” meanwhile, is an observation that has been confirmed repeatedly by different independent researchers. It’s not just one person’s result.
Natural science research is overwhelmingly quantitative. Researchers measure variables, collect numerical data, and use statistical analysis to determine whether their results are meaningful or just noise. This is where mathematics enters the picture. Math isn’t typically classified as a natural science itself (it’s considered a “formal science,” built on abstract logical systems rather than physical observation), but it serves as the essential language of the natural sciences. Every law in physics, every model in chemistry, every population prediction in ecology is expressed mathematically. Mathematical models both describe what researchers observe and guide how measurements are designed and interpreted.
How It Differs From Social and Formal Sciences
Natural science studies nature. Social science studies people: their behavior, societies, economies, and cultures. That distinction in subject matter creates differences in method and structure. Natural sciences tend to build large, concentrated clusters of knowledge where researchers build closely on each other’s findings. A physics paper might receive hundreds of citations from researchers working on tightly related questions. Social sciences operate differently, spreading across many smaller, more isolated pockets of inquiry where novel exploration matters more than following an established thread.
Formal sciences, like mathematics, computer science, and logic, differ from natural science in a more fundamental way. They don’t study anything in the physical world at all. Instead, they work with abstract systems, proving things through internal rules rather than through experiments or observation. You can prove a mathematical theorem with pure logic. You cannot prove that gravity works the same way; you can only observe and measure it repeatedly. That reliance on empirical evidence is what defines natural science and separates it from formal disciplines.
From Natural Philosophy to Modern Science
The term “natural science” is relatively recent. Before the nineteenth century, people doing what we now call science were known as natural philosophers. The tradition stretches back to ancient Greece, where thinkers like Thales, Anaximander, and Anaximenes wrote treatises “concerning nature,” trying to identify the fundamental substance of reality. Thales proposed water, Anaximenes proposed air, and the atomists argued for atoms and empty space.
Isaac Newton’s work cemented natural philosophy as the dominant framework for understanding the physical world for over a century. But eventually, the success of empirical methods led to a split. The study of nature became “natural science,” grounded in measurement and experiment. Philosophy retreated to questions of mind, logic, and knowledge. The older field of “philosophia naturalis,” the philosophy of nature, essentially disappeared. What replaced it on the philosophy side was the philosophy of science: studying how science works rather than studying nature directly.
That transition gave us the modern landscape, where natural science operates through specialized disciplines, each with its own tools and methods, but all sharing a commitment to understanding the physical world through evidence you can observe, measure, and test.