Writing for the Court, Justice Antonin Scalia held that the temporary detention of a motorist upon probable cause to believe that he has violated the traffic laws doesn’t violate the Fourth Amendment’s prohibition against unreasonable seizures, regardless of the officer’s underlying motives. Addressing the argument that police commonly use minor civil traffic infractions as a pretext to investigate unrelated criminal activity, Scalia rejected the premise that an officer’s subjective intentions could invalidate objectively justifiable police conduct, writing that “[s]ubjective intentions play no role in ordinary, probable-cause Fourth Amendment analysis.” Scalia emphasized that while the Constitution prohibits selective law enforcement based on impermissible factors such as race, “the constitutional basis for objecting to intentionally discriminatory application of laws is the Equal Protection Clause, not the Fourth Amendment.” Scalia clarified that prior Supreme Court precedents treating pretext as relevant were strictly limited to inventory searches or administrative inspections conducted in the total absence of probable cause.

Scalia rejected the idea that test evaluating whether a reasonable officer under the same circumstances would have made the traffic stop for the reason given was truly an objective standard. Scalia argued that “although framed in empirical terms, this approach is plainly and indisputably driven by subjective considerations” because its whole purpose was to combat perceived pretext. Scalia explained that Fourth Amendment jurisprudence rejected this approach because “the Fourth Amendment’s concern with ‘reasonableness’ allows certain actions to be taken in certain circumstances, whatever the subjective intent.” Scalia also criticized the workability of evaluating standard police practices across jurisdictions, explaining that “police enforcement practices, even if they could be practicably assessed by a judge, vary from place to place and from time to time,” and declining to accept that “the search and seizure protections of the Fourth Amendment are so variable. . . and can be made to turn upon such trivialities.”

Scalia also rejected the argument that Fourth Amendment reasonableness required courts to engage in a case-by-case balancing of governmental and individual interests for minor traffic stops. Scalia clarified that detailed balancing analysis was necessary only in cases involving seizures executed without probable cause, or in extraordinary circumstances involving searches conducted in an unusual or physically invasive manner, such as the use of deadly force or bodily penetration. Scalia explained that “the making of a traffic stop out of uniform does not remotely qualify as such an extreme practice, and so is governed by the usual rule that probable cause to believe the law has been broken ‘outbalances’ private interest in avoiding police contact.” Applying these principles to the case, Scalia concluded that because plainclothes officers possessed probable cause to believe petitioners had committed traffic violations, “[t]hat rendered the stop reasonable under the Fourth Amendment, the evidence thereby discovered admissible, and the upholding of the convictions by the Court of Appeals for the District of Columbia Circuit correct.”