Moritz Schlick

Positivist · Europe · 1882 to 1936

German-born physicist turned philosopher who was a leader of the Vienna Circle and wrote on space, time, knowledge and ethics.

What it is

Moritz Schlick (1882 to 1936) was a German-born philosopher who trained as a physicist and became a leader of the Vienna Circle, the group of philosophers and scientists known as logical positivists or logical empiricists. He took a close interest in the physics of his day, including relativity and the nature of space and time.

He was born in Berlin and studied natural science in Heidelberg, Lausanne and Berlin, where he worked with the physicist Max Planck. After his doctorate in physics he wrote a treatise on truth and logic, taught at Rostock and then at Kiel. In 1922 he took up a chair in Vienna, the one once held by Ernst Mach and Ludwig Boltzmann, and the Circle gathered around him there.

The main ideas

Philosophy next to science. His training was in physics, and that training stayed with him. He wrote about space and time in the physics of his day.
A theory of knowledge. His General Theory of Knowledge (1918) is one of his major books on the theory of knowledge.
A circle of colleagues. He did not work alone. Philosophers, mathematicians and scientists met around him, among them Rudolf Carnap, Otto Neurath, Kurt Gödel, Hans Hahn and Philipp Frank.
Learning from Wittgenstein. The work of Ludwig Wittgenstein mattered a great deal in the Circle's discussions, and the Circle also drew on the work of Bertrand Russell.
Ethics as a subject. In 1930 he published Problems of Ethics, a book that shows a growing interest in moral questions.

What it looks like in practice

Picture someone in a seminar who hears a bold claim about the nature of space. Following the habit of a physicist-turned-philosopher, she asks what the claim says about measurements and what it would take to show it wrong. If the answer is nothing, she wonders whether the claim says anything yet. This is an illustration of the style of questioning he stood for, not a passage from his writing.

Books and moments

The Nature of Truth According to Modern Logic (1910) was the treatise that helped him win a post at Rostock.
Space and Time in Contemporary Physics (1917) is his book on the physics of his day.
General Theory of Knowledge (1918) is his book on what knowledge is.
Problems of Ethics (1930) is his book on ethics.
A visit to California. He spent time teaching at a university in California in 1929.
22 June 1936. He was shot dead in Vienna by a former student.

Questions and criticism

How closely should philosophy follow the sciences? Schlick's own path, from physics to philosophy, raises the question of whether philosophy can add anything to science or only tidies up after it.
What counts as an answer? If a claim has to be tied to evidence, who decides what counts as evidence, and does that rule itself pass its own test?
Leader or author? He is often described first as the person at the centre of the Circle. Readers can ask how much of its outlook was his own and how much came from the people around him.

Close neighbours

The page on Rudolf Carnap covers a member of the Circle he led, and the page on Ludwig Wittgenstein covers a thinker whose work the Circle discussed closely. The page on Ernst Mach covers the physicist-philosopher whose chair Schlick took.

Written by epchē in our own words, and checked against independent sources on 29 October 2026. The sources are listed below.

Who they connect to

Influenced

Rudolf Carnap · Carnap joined the circle he led and worked out its aims in exact detail.

Influenced by

Ludwig Wittgenstein · He met Wittgenstein often in the late 1920s and took up his view of meaning.

Other Positivist thinkers

Auguste Comte · 1798 to 1857
Herbert Spencer · 1820 to 1903
Ernst Mach · 1838 to 1916
Emile Durkheim · 1858 to 1917
Rudolf Carnap · 1891 to 1970
A. J. Ayer · 1910 to 1989

Sources we used

Moritz Schlick · Stanford Encyclopedia of Philosophy, read on 29 October 2026
Moritz Schlick · Encyclopaedia Britannica, read on 29 October 2026