An alien arriving on our planet would have a hard time understanding who the boss is in the countries of the world. Titles and powers seem to have no consistency and are completely dependent on the country and year.
For example, the United Unites has a president and a vice president but no prime minister. The president has all of the executive powers but delegates funeral visits in foreign countries to the vice-president, probably in application of the principle of out of sight, out of mind. Following the long reign of Franklin Delano Roosevelt, a president is limited to two terms of four years, i.e. eight years of power, which is much healthier for the president and the country.
By contrast, France has a president and a prime minister, but the president has all the powers and changes the prime minister like many women change their hair stylist. After all, someone must be responsible for the high employment and taxes. Designed for the larage ego of General de Gaulle, the term of the presidency is six years and limited to two times, i.e. 12 years, 50% more than in the U.S. As a result of this long exposure to toxic power, most French presidents start believing they are Napoleon. At least, the French president does go to the funerals of foreign leaders, at least most of the time.
England has a prime minister and a royal figure, generally a queen in the last two centuries. The former is the true political leader of the country while the latter mainly handles ceremonial details and provides sufficient material to the tabloids so that the government can do its business without undue interference from the media. This system seems to be more stable than the opposite system used in many European countries until World War I whereby the royal figure had the power and the prime minister was a bit of an errand boy. Granted, Bismarck and Metternich were rather efficient gofers for Prussia and Austria but that was not the rule.
Israel, like France, has a president and prime minister but has the opposite relation. The Prime Minister has the power while the president goes on fun trips abroad and entertains the foreign diplomats. Alas, Israeli presidents in recent decades been very deficient in distracting media attention from the government. On average, elections occur every two years or so. On the other hand, Israel tends to stick with the same prime minister for many years. Apparently, the devil you know is preferable. By contrast, the news generated by the presidents has been less than flattering to Israel. From Ezer Weizman’s politically incorrect comments about various groups in society to Katzav’s conviction for rape, the situation has gone from bad to worse. Fortunately, the current president is humorously irrelevant, a clear improvement. At least, he says the right things.
The confusion gets really thick in Turkey and Russia, where there are presidents that used to be prime ministers. They both had to resign from the latter role because of constitutional terms limits and then got themselves elected as presidents. The situation would be much simpler, if not better, if they just did like many African presidents, elect themselves for life. That way, we all could now who really runs the show.
So, the variations in nomenclature for the 1st citizen of a country are numerous and puzzling. For that matter, we humans seem to like it that way. What difference does it make? There are no visiting aliens anyway, right?