If ever you need a story to back up your advice to students to get someone to proof their work before they submit it, here it is… (my emphasis)
It soon became clear that something had gone very wrong in the text. Rumours swirled, and it was later confirmed by US secretary of state, John Kerry, that the US had objected to Article 4.4 on page 21 of the 31-page final agreement. US government lawyers had found, it was said to their horror, that they had unwittingly approved a vital word which could make the difference between rich countries being legally obliged to cut emissions rather than just having to try to: “shall” rather than “should”.
Here is global law firm Norton Rose Fulbright on the significance of the two words: This article requires developed countries to undertake economy-wide absolute emission reduction targets but developing countries to only “continue to enhance” their mitigation efforts. In the draft that was presented for adoption there were two critical words – “shall” and “should”. The expression “shall” applied to the developed countries’ obligation and the word “should” applied to the developing countries’ obligation. There was a crisis.