The categories are real but not airtight. The president participates in lawmaking through recommendations, presentment, and veto. The Senate participates in appointments and treaties. Courts interpret statutes when deciding cases, and executive agencies interpret law while administering programs. These activities do not erase the branches' principal responsibilities. The question is whether an institution is performing an authorized role within a constitutional sequence or attempting to take final control of a function assigned elsewhere.

A simple example shows the difference. Congress may enact a benefits statute and authorize an agency to determine eligibility under intelligible legal standards. The agency then finds facts and applies the statute to individual claims. A court reviewing a proper dispute may decide whether the agency stayed within the law. Congress supplied the governing rule, the agency administered it, and the court adjudicated the controversy. If Congress tried to decide one claimant's case after the court entered a final judgment, or if an executive officer could revise the court's judgment, the separation problem would be much sharper.

For an exam scenario, begin with a verb. Enacts or appropriates usually signals legislation; administers, enforces, or prosecutes signals execution; decides a case, enters judgment, or reviews legality signals adjudication. Then ask whether another branch is participating through a recognized check or displacing the institution responsible for the final constitutional decision. Cooperation is common. The warning sign is not overlap by itself, but loss of the distinct authority and accountability the Constitution assigns.

Video lesson: Separation of Powers and Checks and Balances: Crash Course Government and Politics #3