practice is sufficient to be bound by it, without signing a treaty. An evolution of the positivist approach of Grotius, the concept of consent is an element of customary international law. Customary international law is essentially what states actually do (state practice), plus the opinio juris of what states believe international law requires them to do. Customary international law applies to every country, regardless of whether they have formally agreed to it. At the same time, all countries take part in forming customary international law by their practices and decisions. As new rules arise, countries accept, reject or modify them. When most countries are following a rule, everyone else will be held to it. Therefore, doing nothing is the same as consenting. Nations that did not take action may find themselves bound by an international law that is not to their advantage. Customary international law can be overruled, however, by a treaty. For this reason, much customary international law has been agreed to formally by treaties between nations. Modern treaty law Treaties are essentially contracts between countries. They are agreements by which the parties intend to be bound. If treaties are broken, their effectiveness is weakened because there is no guarantee that future promises will be kept. So there is a strong incentive for nations to take treaties very seriously. Modern nations engage in a two-step procedure for entering into treaties. The first step is signing the treaty. Being a signatory to a treaty means that a country intends to enter into the agreement. The second step is ratifying the treaty. A country that has ratified a treaty has gone beyond merely intending to enter into the agreement, and is now bound by it. This is a critical distinction, and sometimes a point of confusion. A nation may be a signatory to a treaty for many years without ever having ratified it. Each country ratifies treaties its own way. The United States requires the two-thirds support of the Senate, the upper body of its legislature, for a treaty to be ratified; both the executive and the legislature must agree. In Canada, on the other hand, ratification is strictly an executive action, and no parliamentary approval is required before the nation is bound. Modern treaties are interpreted according to the 1969 Vienna Convention on the Law of Treaties. This convention is so widely accepted that even nations that are not parties