August 26, 2020
Philosophy’s Tetrad Project Awarded International AI Honor
The Tetrad Automated Causal Discovery Platform was awarded the Super Artificial Intelligence Leader (SAIL) award at the World Artificial Intelligence Conference held in Shanghai in July. The Leader award recognizes fundamental advances in the basic theory, methods, models and platforms of artificial intelligence (AI). Tetrad, developed by Peter Spirtes, Clark Glymour, Richard Scheines, and Joe Ramsey of Carnegie Mellon University’s Philosophy Department, was one of four projects chosen for a SAIL award from over 800 nominees, including nominations from Amazon, IBM, Microsoft and Google.
“The Tetrad project, including the open-source Tetrad software package and the now standard reference book …, Causation, Prediction, and Search (1993), are the basis for the modern theory of causal discovery,” said Chris Meek, principal researcher at Microsoft Research. “The ideas and software that grew from this project have fundamentally shifted how researchers explore and interpret observational data.” Causation, Prediction and Search has almost 8,000 citations.
The Tetrad project was started about 40 years ago by Glymour, then a professor of History and Philosophy of Science (HPS) at the University of Pittsburgh (Pitt) and now Alumni University professor emeritus of Philosophy at CMU, and his doctoral students, Richard Scheines, now Bess Family Dean of the Dietrich College of Humanities and Social Sciences and a professor of Philosophy at CMU, and Kevin Kelly, now professor of Philosophy at CMU.
Glymour was fascinated by English psychologist Charles Spearman’s argument for a single “general intelligence,” proposed in the early 20th century, and later work by Hubert Blalock, a sociologist. Both researchers explored the possibility of distinguishing causal models by patterns of constraints they implied on the data. Glymour and his students undertook to generalize that idea, turn it into a computer algorithm and explore related mathematical properties.
The first version of the Tetrad program became the basis of Scheines’ doctoral research, which required him to learn as much computer science and statistics as philosophy, an interdisciplinary approach that was encouraged at CMU, where Scheines joined the faculty in 1988.
Peter Spirtes, who also received his PhD from HPS at Pitt and is now a Professor in CMU’s Philosophy Department, joined the project while taking a Master's degree in computer science at Pitt following his doctoral work. A number of doctoral students at CMU have based their work around the Tetrad project.
Fundamental to the work was providing a set of general principles, or axioms, for deriving testable predictions from any causal structure. For example, consider the corona virus. Exposure to the virus causes infection, which in turn causes symptoms (Exposure --> Infection --> Symptoms). Since not all exposures result in infections, and not all infections result in symptoms, these relations are probabilistic. But if we assume that exposure can only cause symptoms through infection, the testable prediction from the axiom is that Exposure and Symptoms are independent given Infection. That is, although knowing whether someone was exposed is informative about whether they will develop symptoms, once we already know whether someone is infected or not – knowing whether they were exposed adds no extra information - a claim that can be tested statistically with data.
Spirtes, Glymour and Scheines then turned this kind of reasoning on its head and extended it to massively complex causal systems. They developed algorithms that take measured data and background knowledge as input, and then compute the set of underlying causal systems that might have produced specific patterns in the measured data. What can the algorithms tell us about the causal system that underlies the measured data? According to Scheines, “not everything, but in some cases quite a lot.” Spirtes led the effort to prove that the algorithms were theoretically reliable. This approach to causal discovery constituted a breakthrough in fundamental methods in AI.
The next step was to make the work practical – which required efficient algorithms and massive amounts of simulation and real scientific testing. In the late 1990s, Joe Ramsey joined the team as a systems developer, and he has developed several important algorithms, and has made many others dramatically more efficient. With help from Spirtes, Glymour, Scheines, and many others, Ramsey developed the Java-based Tetrad platform, which supports model building and testing, full simulation, and implements dozens of causal discovery algorithms that can be executed on one’s laptop or on the Bridges Pittsburgh Supercomputer.
Over the last 15–20 years, the free, open-source software platform has been successfully applied to scientific problems from economics to psychology to educational research to neuroscience by the original team and by researchers around the world. In 2013, the Tetrad team joined Greg Cooper and others at the University of Pittsburgh and received a NIH Big Data to Knowledge Center Grant to form the Center for Causal Discovery, which led to software improvements and a variety of new algorithms for special problems.
“We couldn’t have done this [type of work] at almost any place but CMU,” said Scheines. “Most institutions would not have allowed philosophers to be so heavily interdisciplinary, and none would have hired three philosophers who collaborated closely on the same project for most of their careers. Clark Glymour, who founded the CMU philosophy department in 1985, had a vision for a completely different sort of department, which Dick Cyert and Herb Simon supported fully, and which came to be. Peter, Kevin, and I were lucky enough to come along just when it started.”
“Causality, with its focus on modeling and reasoning about interventions, can … take the field [of AI] to the next level. …. the CMU group including Peter Spirtes, Clark Glymour, Richard Scheines and Joseph Ramsey was at the center of the development, not just in terms of algorithm development, but crucially also by providing Tetrad, the de facto standard in causal discovery software,” said Bernhard Schölkopf, Amazon Distinguished Scholar and chief machine learning scientist and director, Max Planck Institute for Intelligent Systems in Germany.