The Republican platform in 1908, in view of the changing public sentiment, formulated a new rule for maintaining "the true principle of protection," namely, that it "is best maintained by the imposition of such duties as will equal the difference between the cost of production at home and abroad, together with a reasonable profit to American industries." This rule is very attractive in its suggestion at the same time of the idea of a moderation of the tariff and of an exact practical (not to say scientific) standard for the determination of the proper rate in every case. The rule is, however, fallacious. "Costs of production" mean here the monetary costs of the enterpriser. Now a first difficulty is that costs are not uniform for all establishments in any one industry, and a tariff high enough to protect some is entirely too low to protect others. As long as a tariff rate is too low to exclude every unit of the foreign product its importation is conclusive proof that for some home producers the tariff rates fall short of the "true principle" (better proof, indeed, than the most elaborate investigation by any tariff board could be). The indubitable truth is that no trade ever can take place (in a monetary régime) unless the monetary price is lower in the exporting than it is in the importing country. This virtually means that the product cannot be profitably exported unless the monetary costs of production ("together with a fair profit") of the article exported are for each party less than those of the other party in the other country.[9] The so-called "true principle" would lead thus to absolute prohibition of every article to which it was applied.