When Emerson introduces the idea that everyone has a stable, inborn "temperament" on which all the "colored beads" of their experience are strung, he nonetheless rejects the idea that human behavior is predictable. He uses a metaphor and logos to explain why:
Shall I preclude my future, by taking a high seat, and kindly adapting my conversation to the shape of heads? When I come to that, the doctors shall buy me for a Cent.—“But, sir, medical history; the report to the Institute; the proven facts!”—I distrust the facts and the inferences. Temperament is the veto or limitation-power in the constitution, very justly applied to restrain an opposite excess in the constitution, but absurdly offered as a bar to original equity.
Emerson is referring to the pseudoscience of phrenology, by which some scientists and doctors claimed to be able to predict someone's personality and capabilities by observing the shape of their head. Phrenology is a big part of the history of scientific racism, or the use of pseudoscience to prop up the ideology of white supremacy. Emerson's idea of an inborn temperament at first seems to support the idea, central to phrenology, that people's capabilities are determined from birth. However, Emerson argues that every person contains multitudes that no one can see from the outside. He "distrust[s] the facts and inferences" of phrenology because someone's temperament can never really be observed in full.
He compares temperament to "veto or limitation-power in the constitution." He is playing with words here: he is referring to the legal constitution that forms the basis of the United States government, but he is also referring to the "constitution" of an individual—that is, the way they behave based on both nature and nurture. Under the United States constitution, the three branches of government are meant to "check" one another, limiting the ability of a single branch to exert excessive power. This does not mean that any branch is powerless. Rather, it means that they are all (theoretically) balanced. Emerson argues that an individual's "constitution" operates the same way. Their innate temperament is a "check" on their constitution, perhaps making them predisposed to certain behaviors like daydreaming rather than focusing on their work. But it does not outright "bar" them from any behavior; for instance, the same person might undergo schooling that teaches them to be a highly focused person. By comparing a person's constitution to the U.S. constitution, Emerson demonstrates that human capacity is not determined from birth.
