Alois Adolf Riehl (German: [ʀiːl]; 27 April 1844 – 21 November 1924) was an Austrian philosopher. He was born in Bozen (Bolzano) in the Austrian Empire (now in Italy).
The brother of Josef Riehl, he was a Neo-Kantian and worked as a full professor of philosophy at Graz from 1878, then at Freiburg (from 1882 as a replacement for Wilhelm Windelband), and finally in Berlin, where he commissioned Mies van der Rohe to design his house in Neubabelsberg.
For Riehl, philosophy was not the teaching of Weltanschauung, but principally a criticism of perception.
Riehl died in Neubabelsberg, near Potsdam, and was buried in the Alter Friedhof in Klein-Glienicke.
His wife Sofie, was the aunt of Frieda Gross, the wife of the Austrian medical doctor, scientist and revolutionary, Otto Gross.
- Der Philosophische Kriticismus und seine Bedeutung für die positive Wissenschaft, 1876 – Philosophical criticism and its importance for the positive science.
- Beiträge zur Logik, 1892 – Contributions to logic.
- "The principles of the critical philosophy", 1894 (translated into English by Arthur Fairbanks) London, K. Paul, Trench, Trübner, & Co., Ltd, 1894.
- Friedrich Nietzsche, der Künstler und der Denker, 1897 – Friedrich Nietzsche: the artist and the thinker.
- Zur Einführung in die Philosophie der Gegenwart, 1903 – An introduction to the philosophy of the present.
- Systematische philosophie, 1907 (with Wilhelm Dilthey) – Systematic philosophy.
- Der philosophische kritizismus, geschichte und system, 1908 – Philosophical criticism, history and system.