"Our tax system is based upon voluntary assessment and payment and not upon distraint." Supreme Court Ruling, Flora v. U.S., 362 U.S. 145

"Our tax system is based on individual self-assessment and voluntary compliance." M. Caplin, IRS Commissioner

26 CFR § 601.602 - Tax forms and instructions.

(a) Tax return forms and instructions. The Internal Revenue Service develops forms and instructions that explain the requirements of the Internal Revenue Code and regulations. The Service distributes the forms and instructions to help taxpayers comply with the law.The tax system is based on voluntary compliance, and the taxpayers complete and return the forms with payment of any tax owed.