Boyd v. U.S., 116 U.S. 616, 635 (1886):
Illegitimate and unconstitutional practices get their first footing . . . by silent approaches and slight deviations from legal modes of procedure. This can only be obviated by adhering to the rule that constitutional provisions for the security of person and property should be liberally construed. A close and literal construction deprives them of half their efficacy, and leads to gradual depreciation of the right, as if it consisted more in sound than in substance. It is the duty of courts to be watchful for the constitutional rights of the citizen, and against any stealthy encroachments thereon. Their motto should be obsta principiis. We have no doubt that the legislative body is actuated by the same motives; but the vast accumulation of public business brought before it sometimes prevents it, on a first presentation, from noticing objections which become developed by time and the practical application of the objectionable law.