John Everard is a former British ambassador to North Korea and a former adviser to the UN. The opinions in this article belong solely to the author.

(CNN) In a war of words, like the one in which the USA is currently engaged with North Korea, it is essential to use those words effectively. But President Donald Trump is mangling the US's ability to do so.

In such an exchange, each state needs three aspects of its words to do three things.

Their substance needs to convey exactly what that state means, their register needs to convey how relaxed or how angry it is, and the rank of their speaker needs to show how much authority they carry.

North Korea is careful on all three points. It expresses itself in uniquely colorful terms, but it usually uses standard phrases with quite precise meanings and deviates from these phrases only to signal a change in its thinking. The same goes for register.

Near-hysterical opprobrium of the US is routine and changes in the flamboyant language signal shifts in mood. Paradoxically this means that sometimes when North Korea is really angry, its language is almost sober. And it uses a carefully graded system of speakers to indicate how firm its statements are. At the bottom of the scale, remarks by unnamed state media commentators are often just trial balloons. At the top, any remark attributed to Kim Jong Un is scripture, unchangeable and non-negotiable.

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