Different forms of representation
The House of Representatives is built around local electorates. Each member represents one geographic division, so changes in population affect electoral boundaries and the distribution of seats. The Senate is designed around representation of states and territories. States receive equal numbers of senators even though their populations differ greatly.
That design means the chambers answer different democratic questions. The House asks which candidates can win individual electorates and which political grouping can command a majority of members. The Senate gives voters a multi-member contest and often produces a more politically diverse chamber.
Government is formed in the House
The party or coalition that can command majority support in the House forms government. Its leader normally becomes Prime Minister. A government must retain the confidence of the House to remain in office. This is why election-night coverage focuses heavily on the number of House seats won or likely to be won.
Winning more Senate seats than an opponent does not by itself allow a party to form government. The Senate can be politically powerful, but government formation is tied to confidence in the House.
The Senate can reshape legislation
Most proposed laws must pass both houses in identical form. The Senate can agree to a bill, reject it or seek changes. If the Senate amends a bill that originated in the House, the House must consider those changes. Negotiation can continue until the houses agree or the proposal fails to progress.
This is why the composition of the Senate matters even after a decisive House election result. A government without a Senate majority may need support from the opposition, minor parties or independents to pass contested bills.
Money bills are a special case
The Constitution places restrictions on the Senate concerning laws that appropriate money or impose taxation. Such bills cannot originate in the Senate, and the Senate cannot amend certain classes of financial legislation in the same way it can amend ordinary bills. It can, however, request amendments in circumstances provided for by the Constitution.
These rules are one reason descriptions such as 'the Senate is weaker' or 'the houses are equal' are both too simple. The Senate has extensive powers, but not identical powers in every category of legislation.
A useful way to read parliamentary headlines
When a story says a bill 'passed Parliament', check whether both houses have agreed to the same text. When it says the government 'has the numbers', ask whether that refers to the House, the Senate or a specific vote. A government may have a reliable House majority while facing difficult negotiations in the Senate.
Those distinctions often explain why a policy announced during an election campaign changes during the legislative process. The final law can reflect amendments, compromises and committee scrutiny that occurred after the original announcement.
Primary sources and further reading
We use authoritative Australian institutions as the starting point for this explainer. Follow these links for the underlying rules, official guidance and current details.