(Fourth in The interpretation of statutes and the denial of judges' power series.)
The first concern when evaluating textualism and purposivism against constitutional imperatives is whether talk of "the correct interpretation of constitutions and statutes" is even meaningful. Even if comparison against an objective standard is possible, why does it matter whether the interpretation is correct when the better policy contravenes the so-called correct interpretation? As I am more enthusiastic about the dictates of democracy than the specifics of the U.S. Constitution, what significance should it have, as I will claim, that a form of textualism better expresses constitutional imperatives? My hypothesis is that the correct interpretation of the constitution is significant not because constitutional statutes make better policy but because all else being equal the sequence of judicial interpretations tends to approach the constitutionally correct interpretation. The underlying metaphor is of the correct interpretation representing a constant force acting, like gravity, on the statute's interpretation, and, also like gravity, the force increases as the interpretation enters the correct interpretation's neighborhood.
This interpretive improvement takes place both by assimilation and accommodation. The accommodative version is straightforward. The law moves progressively closer to the correct interpretation. In the assimilative convergence, other laws are interpreted based on the (initially wrong) interpretation, so that what was legally wrong becomes right, as law establishes coherence with (initial) error, creating new masses counteracting the original gravitation pull.
Brown v. Board of Education illustrates by containing divergent possibilities. After Plessey v. Ferguson, separate but equal became entrenched throughout the law, and the segregationist interpretation of the 14th amendment became more legally right with time, not less right, like a "Living Constitutionalist" might say. The interpretation yet remained inferior to the plain-meaning interpretation: separate is not equal because separate means different with respect to spatial disposition, and equal means the same in every respect. When an interpretation really is true by plain meaning, almost nothing can overcome it. So when there intervened other circumstances — such as international revulsion at American racism — seizing on the integrationist interpretation was easy, even though court unanimity allowed only a superficial empirical argument, rather than a broadly applicable (and more correct) plain-meaning one.
Correct interpretations should exert an attractive force that actual law approaches at the limit, but the question of degree can't be resolved at so general level of argument. The degree of interpretive pull the correct view exerts depends partly on the push of the correct method: will judges converge on a version of textualism? We now turn to why the U.S. Constitution is textualist.