Principle of Equal rights for nationals and foreigners
In international relations and treaties, the principle of reciprocity expresses that legal benefits or rights that are granted by one state to the citizens or legal entities of another, are granted under the condition that the other state grants the same legal benefits or rights to the citizens or legal entities of the first state. This is however not exactly the same as the provisions in the Paris convention that equal rights for protection must be granted to foreigners of another Union state as they are granted to the citizen or enterprises of the same state.
In order to understand the difference let's look at the social behaviour of reciprocity and later on the legal principle of reciprocity
The principle of reciprocity seems to exist for a long time, without having been codified. The principle of reciprocity is a social behaviour, that securs, for example, trade between people. Letting a trade caravan pass without confiscating the goods, is a form of reciprocity that allowed the exchange of goods over the national borders of multiple territories for the benefit of
the country the goods are coming from (extra profits by selling goods outside the home market)
the country that receives the goods (access to luxury goods, such as pepper or silk, which could not be produced in the home country)
the countries that allow the goods to transit (income from tariffs levied on the transiting goods)
The long time benefit of constant income outweighs the temptation of a one-time opportunity to seize the goods.
The Britannica defines reciprocity in trade as:
In a trade agreement, the parties make reciprocal concessions to put their trade relationships on a basis deemed equitable by each. ... The concessions may, however, be in different areas. In the Anglo-French Agreement of 1860, for example, France pledged itself to reduce its duties to 20 percent by 1864. In return, Britain granted duty-free imports of all French products except wines and spirits. The principle of reciprocity implies only that the gains arising out of foreign trade are distributed fairly.
One of the earliest forms of reciprocity, if not the earliest at all, codified in a patent law, was the Act for amending the Law for granting Patents for Inventions of 1st July 1852 for the United Kingdom of Great Britain and Ireland.
Patent Act 1885, Paragraph XXVI
No Letter Patent for any Invention (granted after the passing of this Act) shall extend to prevent Use of such Inventions in any Foreign Ship or Vessel, or for the Navigation of any Foreign Ship or Vessel, of for the Navigation or any Foreign Ship or Vessel, which may be in any Port of Her Majesty's Dominions, or in any of the Waters within the Jurisdiction of any of Her Majesty's Courts, where such Invention is not so used for the Manufacture of any Goods or Commodities to be vended within or exported from Her Majesty's Dominions: Provided always that this Enactment shall not extend to the Ships or Vessels of any Foreign State of which the Laws authorize Subjects of such Foreign State, having Patents or like Privileges for the exclusive Use or Exercise of Inventions within its Territories, to prevent or interfere with the Use of such Inventions in British Ships or Vessels, or in or about Navigation of British Ships or Vessels, while in the Ports of such Foreign State, or in the Waters within the Jurisdiction of its Courts, where such Inventions are no so used for the Manufacture of Goods or Commodities to be vended within or exported from the Territories of such Foreign State.
Act for amending the Law for granting Patents for Inventions of 1st July 1852 for the United Kingdom of Great Britain and Ireland.
The original Article 2 of the earliest version of the Paris Convention reads as follows:
Article 2 Paris Convention (original version of 1883)
The subjects or citizens of every Contracting State enjoy in every other State of the Union, as far as it concerns patents, designs and industrial models, trademarks and trade names the advantages that the respective laws grant at the moment or will grant in future to their nationals. Consequently, they shall have the same protection as these and the same legal remedy against any infringement of their rights, provided they observe the formalities and conditions imposed on nationals by the domestice legislation of each State.
Unofficial translation of the orignal French text
The accession of the U.S. in 1887, allowed foreigners, which were citizens of the Union member states, to file in the U.S. at the same conditions as a U.S. citizen. It is therfore a perfect scenario for comparing the economical effects, as there were many other economical powerful countries left, who were not part of the Union and did not grant same rights for foreigners and citizens.
The U.S. accession strengthened U.S. patent rights for nationals from countries that had signed the treaty before the United States, but had no effect on nationals from other countries. An analysis of 86,000 U.S. patents between 1865 and 1914 indicates that nationals from the original member countries increased their patenting activity in the United States by more than 40 percent after U.S. accession compared with nationals from other countries. Importantly, the effects of the treaty were strongest for nationals from countries with high pre-treaty levels of development and education, that were most able to respond to stronger property rights.
Do Treaties Encourage Technology Transfer? Evidence from the Paris Convention L. Kamran Bilir, Petra Moser, and Irina Talis, May 19, 2011