The major cause are what is know as Russell’s "propositional* functions", i.e. sentences which do not actually constitute logical sentences, but are more similar to algebraic functions with several meanings.
It is indicative that some semantic researchers refer to unclearly expressed propositional* functions as "noise", for neither the speaker nor the listener know what the sentence really means. But as in a band of monkeys, noise also creates feelings such as anger and fear, and therefore aggression, in people.
In this connection let me point out that in the 19th Century, John Highlings Jackson coined the term propositional* to characterise the dominance of the left brain hemisphere when speaking, in the sense that it thinks in terms of propositions, i.e. statements.
*In contrast to the term "propositional", Joseph Bogen, one of the pioneers of commissurotomics, coined the word "appositional" to characterise the processing of information in the right brain hemisphere of right-handed people with pronounced lateralisation, and was emphatic in his belief that appositional thinking should be developed and encouraged in schools. One German proponent of appositional thinking in schools (I am grateful to Karl "The Guv’nor" Koch for pointing this out) is Dr. Gerhard Huhn (Creativity and School, the risks of current curricula for the free development of children - unconstitutionality of government policies relating to educational goals and teaching content in the light of the latest findings in brain research).

"To be" or not "to be"

There are strong arguments for dispensing with the verb "to be" (and all its forms such as "am", "is", "are", "was", "will be" etc.) in every verbal and written expression, but especially in thought.
Before you write me off as a madman – which I would see as a compliment - let me briefly discuss the philosophical and psychological reasons for this.
As somebody who has experienced the Taoist philosophy in more than forty years of physical work and meditation, let me first take aim at the classic Aristotelian axiom of sameness or identity.
Like Heraclitus, another Greek philosopher, I believe that we never step into the same river twice, but that everything is constantly in flux and always changing. The moment I see e.g. a "Bong-Sao" technique and call it that, it has already changed to something else.
The same applies to people or things. The statement that "Peter is stupid" robs Peter of his intelligence to the end of his days and compartmentalises him, whereas the speaker only wanted to say that in a particular case, Peter did not behave as the speaker expected a sensible person to behave. No wonder that Peter might react with anger. Another sentence which has a no less harmful effect as a self-fulfilling prophesy is e.g. "I have always been bad at expressing myself", as it prevents the person who speaks or thinks in this way from finding the courage to write an important letter – perhaps for life. And all because he was once given a poor mark in English language at school. In fact I myself was given a 6 (the worst mark) in German in the 3rd form at school, and a 1 (the highest) for my leaving examination – with the same teacher as the second examiner, I might add.
Using the verb "to be" conjures up ideas of eternity, permanence and rigidity. Anybody who speaks and therefore thinks in this way is creating an artificial, dead world in which there is no change and no hope. Somebody who e.g. thinks of himself that "I am a fighter" robs himself of any future and any possibility of further development. For he either "is" a fighter or he "is" not at all. The word "is" only allows pairs of opposites such as yes or no, no middle way and no intermediate stages of change as in nature. If a young man takes pleasure in overcoming resistance and fighting, this is only a brief development phase in his life. As he grows older he must realise that "fighting" always means "against", and that every "against" goes against nature, existence and therefore himself. Because he thinks of himself as a "fighter" and others therefore expect a corresponding behaviour of him, he is unable to escape from the prison of his own self-programming ("A man has to do what a man has to do." ).
Giving things names and saying that something is this or that is equivalent to an act of aggression against oneself and others. Calling a lion a "beast of prey" and a slave "good" not only says something about the development of our so-called "moral" ideas, but controls our thinking more than we realise. The statement "That is the truth" tries to assert that there is such a thing as "the" truth. Without the terrible verb "to be" we would be unable to compare ourselves, there would be less envy and aggression and we could not even ask ourselves: "Who is the best fighter?".
The conversation-stopper "That film was fantastic" would then become the subjective, debatable opinion "I found that film superb because …". And there would no longer be the life-threatening passive form ("450 000 cattle had to be killed as a result of the X-epidemic" or Ronald Reagan: "Mistakes were made") behind which the speaker (the subject of an active sentence) can hide unmentioned. We would become rather more aware of our responsibilities and no longer see ourselves as victims threatened by an anonymous world ("I have been dismissed from my job"), but rather take personal charge of our lives.
Whenever* we use a form of "to be" we are lying to ourselves or others. So be wary if you read, hear, think or speak any form of the verb "to be".
I find the identifying function of "to be" particularly dangerous and ambiguous: "Fear is the best teacher" (Fear - the best teacher?), or its use as a description: "The lemon is yellow". (In fact yellow is not a characteristic of the lemon, for only healthy human eyes perceive it as yellow. The colour-blind would see it as grey.) From his study of colours, Goethe recognised something of which leading scientists are nowadays convinced: the observer not only changes but in fact creates the world by observing.
If you see somebody staggering out of a public house and say to yourself:
"He’s drunk", he can expect no assistance from you. But if you reformulate your thoughts to: "He gives an impression of being drunk", then your doubt might induce you to look more closely and save the life of a potential victim of violent crime. Let us always be aware that every sentence we even think tries to become reality and programmes us. You are what you think of yourself .
But other people are also what you think of them! So let’s be careful about placing these "orders", and any form of propositional statement.
If somebody says to you "That’s a silly idea", you could translate this into "to be-less" language (D1) for yourself and ask "What don’t you like about it?" rather than answering "Nonsense, it’s a good idea but you’re too stupid to see it!" If someone abuses you by saying "You’re an idiot!", take a step back and translate this into D1: "You have really annoyed me!".
If you are confronted with a problem and think: "That’s impossible", it is better to think "It appears impossible to me at present", and then find a solution.
Incidentally, there are apparently languages which dispense with "to be", namely Mandarin, Russian and Hungarian, and I have also done my best to write this article in D1 (with the exception of quotations etc.).
The English infinitive "to be" is derived from the Sanskrit (the ancient language of Indian scholars) root "bhu", which means to make grow or grow. In the 1st or 3rd person present singular "am" and "is" we find the same root as that of the Sanskrit word asmi = breathe. Those fortunate people in those days had no word for "to be" yet!
Buddha was right when he prescribed "correct speaking" as a recipe for overcoming suffering ("On Single Combat", p. 260).