Rudy Giuliani recently exclaimed “truth isn’t truth” in a televised interview. He is part of an administration that has made thousands of false claims. But what is truth that is so badly disrespected by these utterances?

Another disrespecter of truth is Jordan Peterson, who says that “Mythological renditions of history, like those in the Bible, are just as “true” as the standard Western empirical renditions.” I have critiqued his view of reality in commenting on his books Maps of Meaning and 12 Rules for Life. Peterson frequently attacks post-modernists for their views on and , but he shares with them the assumption that truth is relative to personal and social .

The alternative is what philosophers call the correspondence theory of truth: a belief is true if it describes the world accurately. Alternative theories include the coherence theory, according to which the truth of a belief is just how well it fits with other beliefs, and the social construction view that truth is relative to what people want. My forthcoming book, Natural Philosophy, provides reasons why the correspondence theory of truth is far more plausible than its alternatives.

Coherence is a criterion for truth, not truth itself. Identifying truth with coherence fails because there are opposing views that are each internally coherent even though they do not agree with each other. For example, the Mormon religion and Scientology are complex worldviews full of internal coherence, but they are not compatible with each other and with scientific findings.

Science settles disagreements by comparing competing theories based on evidence that results from systematic interactions with the world through scientific experiments. Experiments and systematic observations provide a grip on the world because the results are partly caused by interactions with objects and their properties.

Science and truth are not mere social constructions. In both science and everyday life, people do not get to build the worlds they want, because they are constrained by physical, chemical, and biological reality. For example, it would be wonderful to create a world in which everybody enjoys wealth and longevity, but physical limitations such as the amount of resources on the planet and biological limitations such as cell death make it difficult to construct what people want.

A challenge to scientific truth comes from the observation that all of our scientific theories resulted from the operations of minds and social groups, so it might seem that reality is mind-dependent or socially constructed. But the need of science for mental and social activity does not undercut the conclusion that science finds out about the world. Here are three kinds of evidence supporting this inference.

First, scientific experiments are remarkably resistant to the desires and efforts of scientists. Many failures and surprises show that experimenters cannot detect whatever they want, because instruments and other forms of observation are strongly constrained by their interactions with the world. If coherence or social construction were right about truth, experimental science would be a lot easier than it is because minds could just get together to construct the reality they want.

The obstinacy of experiments is that the world often resists scientists’ attempts to get the experimental results that would confirm their expectations. As of 2018, physicists are largely convinced that most of the universe’s mass consists of dark matter because of its gravitational effects, but experimental efforts to detect it directly have repeatedly failed. If the world were just socially constructed, scientists should have been able to avoid such failures.

Second, science is unusual compared to other social enterprises such as religion and fashion design in having a remarkable amount of agreement among its practitioners. Although there are many controversies in physics, chemistry, and biology concerning the best theories, there is also remarkable agreement about central theories such as relativity and quantum theory in physics, and evolution and in biology. This agreement allows science to be cumulative, building progressively on the results of previous generations, even though theoretical revolutions occasionally occur with substantial conceptual change.

Third, science has been dramatically successful in spawning technology, such as spacecraft, computers, and antibiotics. These operate with theoretical hypotheses such as gravity, electrons, and viruses. Without supposing that these hypotheses are approximately true of a world independent of us, we have no way of explaining why technology works as it often does, and why there are sometimes technological failures despite the best efforts of minds and groups. Building technologies requires understanding the world’s physical mechanisms that are largely independent of mind and society.

For all these reasons, we are justified in concluding that truth is correspondence to reality, and in scorning politicians and pundits who disrespect truth in favor of ideological motivations.