Let's hear from Zamenhof himself how he came to invent Esperanto, more than one century ago. He is describing the context in this letter to a friend.
It is not easy for me to relate all this in detail to you, because much I have already forgotten; the idea to whose realization I have dedicated my whole life, appeared to me - ridiculous as it may seem to say so -in my earliest infancy, and from that time it has never left me. I lived with it and I could never imagine myself without it. This will explain to you why I with so much constancy worked over it and why I, in spite of ail difficulties and unpleasantness, never gave up the idea, as many others working in the same field have done.

Of course I became convinced by degrees that not everything is as easy as it seems to a child; one after another I put aside various Utopias of my boyhood and only the dream of a single common language for humanity I never could cast aside. In some unexplainable way I was attracted to it, though, of course, without any definite plans. I do not remember when, but in any event very early, I became conscious that the one language should be absolutely neutral, belonging to none of the now-living tongues. When, from the Bielostok high school I entered the Classical Academy in Warsaw, I was for some time attracted to the ancient languages, and dreamt that some day I should travel about the world and with fiery words persuade the nations to revive one of these languages for common use. Afterwards, I do not remember just how, I arrived at the firm conviction that this was impossible and commenced dimly to dream of a new, artificial language. I then began many attempts, invented artificial declensions and conjugations, etc. But a human language with its seemingly endless mass of grammatical forms and hundreds of thousands of words (with which the big dictionaries terrified me) seemed such an artful and colossal machine that I more than once cried, "Away with dreams! This work is beyond human power." All the same, I always came back to my dream.
The German and French languages I learned in childhood when it was still impossible to make comparisons or arrive at conclusions; but when in the fifth class of the Academy I began the study of English, the simplicity of the English grammar was striking, especially with the sudden change from the Latin and Greek grammars. I remarked then that the multitude of grammatical forms is only a chance historical incident and with no logical linguistic necessity. Under the influence of this idea, I began to look into my language and to throw away the needless forms. I remarked that the grammar ever more and more melted away in my hands, and that it soon arrived at a form so simple that, with no damage to the language, it occupied no more than a few pages. Then I began more seriously to devote myself to my dream. But the prospect of the big dictionaries still left me always disquieted.
Once, when I was in the sixth or seventh class of the Academy I happened to have my attention drawn to the inscription" "Svejcarskaja", which I had seen many times, and later on, the sign "Konditorskaja ". I became interested in this "skaja", and I saw that the suffixes gave me the possibility of making out of one word other words which would not have to be learned separately. This thought quite captured me and I suddenly found the ground under my feet. Upon the stupendous dictionaries fell a ray of light and they rapidly began to shrink before my eyes.
"The problem is solved!" I said. I took the idea of suffixes and began working at great length in that direction. I realized what great significance for a consciously created language is possessed by that power which in natural languages works only partly, blindly and irregularly. I began to compare words, to seek among them for constant and definite relations, and every day I eliminated from the vocabulary a new, long series of words, replacing it with one suffix which signified a certain relationship. I noticed then that a great mass of root-words (for example, "mother", "narrow", "knife", etc.) could be easily replaced by derived words and disappear from the dictionary. The mechanism of the language was before me as though upon the palm of my hand and I now began to work regularly with love and hope. Soon after that I had written the whole grammar and a small vocabulary.
Here I will say something about the material for the dictionary. Much earlier, when I sought and threw out everything unnecessary from the grammar, I wished to use the principles of economy also for the words, and, convinced that it is immaterial what form is taken by this or that word (if we only agree that it expresses the idea in question), I simply invented words, endeavoring to make them as short as possible and without needless letters. I said to myself, that instead of the eleven-letter 'interparoli', for example, I can express the same idea by the two-letter 'pa'. Therefore, I simply wrote the mathematical series of the shortest, but easily-pronounced combination of letters, and to each gave the meaning of a definite word (for example, a, ab, ac, ad, - ba, ca, da, - e, eb, ec, - aba, aca, etc.). But this thought I immediately discarded, for the tests with myself showed me that such invented words are learned with difficulty and with even more difficulty remembered. Already then I became convinced that the material for the vocabulary must be Romance-Germanic, changed only as much as would be required by the regularity and other important conditions of the language.
From this standpoint I soon noticed that the existing languages possess an immense storehouse of ready words, already international, which are known to all peoples and form a treasure for the future international language and I, of course, utilized this treasure.
In the year 1878 the language was already more or less ready, although between the then "Lingwe uniwersala" and the present Esperanto there was still a great difference. I spoke of it to my colleagues (I was then in the eighth class in the Academy). Most of them were attracted by the idea, and by the strikingly unusual simplicity of the language, and began to study it. On the 5th of December, 1878, we all gathered to celebrate the consecration of the language. During this event there were speeches in the new tongue, and we enthusiastically sang the hymn whose opening words are as follows:
"Malamikete de las nacjes
Kadó, kadó, jam temp; está!
La tot' homoze in familje
Konunigare so debá."
(A free translation in English would be: "Let the hate of the nations fall, fall! The time is already here. Humanity must unite in one family.)
Upon the table, along with the grammar and the vocabulary, were several translations into the new language.
Thus concluded the first period of the language. Since I was then still too young to come out publicly with my work, I decided to wait another five or six years and during this time carefully to test the language and work with it fully in practice. Six months after the celebration of the 5th of December we finished the Academy course and separated. The future apostles of the language tried to talk about the 'new speech' to others, but, meeting the ridicule of older people, they at once hastened to disown it, and I was left entirely alone. Anticipating only mockery and persecution, I decided to hide my work from everyone. During five and a half years of my stay in the University, I never spoke to anyone about the matter. This period was for me very difficult. The secrecy tormented me. Being obliged to hide my thoughts and plans, I hardly went anywhere or took part in anything, and the most beautiful time of life - the years of a student - for me passed most sadly. I sometimes tried to seek diversion in company, but, feeling myself always a stranger, I sighed and went away. Sometimes I eased my heart by composing verses in the language. One of these poems, "Mia Penso", I added to the first booklet issued by me; but to the readers who know nothing of the circumstances in which these verses were written, they seemed, of course, strange and incomprehensible.

During six years I labored, perfecting and proving the language - and in this I had enough work, although in the year 1878 it seemed to me that the language was already in finished shape. I translated much and wrote original pieces in it, but extensive tests showed me that that which seemed to me to be ready in theory was still not ready in practice. Much I was obliged to prune away or to find substitutes for, to correct and radically to transform. Words and forms, principles and requirements pushed and hindered one another, while in theory each thing separately and in short tests seemed to me quite good. Such things as, for example, the universal preposition "je", the elastic verb "meti", the neutral but definite termination "au", etc., of course, never would have fallen into my head as a matter of theory. Certain forms which originally seemed enriching now appeared in practice to be unnecessary ballast. Thus, for example, I had to discard certain useless suffixes. In the year 1878 it seemed to me enough that the language should have a grammar and a vocabulary; the heaviness and clumsiness of the language I ascribed only to the fact that I had not yet fully mastered it. Practice, however, more and more convinced me that the language still needed an elusive something, a binding element, giving to the language life and a definite, concrete spirit. (Ignorance of the spirit of the language is the reason why some Esperantists, having read very little in Esperanto write without error but in a clumsy, ungraceful style, -while more experienced Esperantists write in good style, exactly the same, whatever the nation to which they belong. In the course of time the spirit of the language will change, without doubt, although by insensible degrees. But if the first Esperantists, people of diverse nations, had not seen in the language a quite definite fundamental spirit, each would have begun to follow his native style and the language would have remained forever, or at least through a long period, a clumsy and lifeless collection of words.) I began then to avoid literal translations of this or the other tongue and tried to think directly in the neutral language. Then I noticed that the language in my hands already ceased to be a baseless shadow of this or the other language. that it possessed its own spirit, its own life, its own definite and clearly expressed physiognomy, independent of outside influences. The words flowed of themselves, flexibly, gracefully and quite freely, like a living mother tongue.
Still one circumstance caused me for a long time to postpone my bringing out the language. For a long time there remained unsolved a problem which has great significance for a neutral tongue. I knew that everyone would say to me: "Your language will be useful to me only when the whole world accepts it; therefore I cannot accept it until the whole world accepts it." But because the "world" is non-existent without already-existing units, the neutral language cannot have a future until it shows itself useful to each separate person, whether or not it has already been accepted by the world. I thought for a long time over this problem. Finally, the so-called secret alphabets gave me the clue. These do not require a previous acceptance by the world, but give to an addressee, even without prearrangement, the ability to understand everything you write, if you only send him a "key". This led me to the idea of arranging the language also in the manner of a "key", which should contain, not only the whole vocabulary, but also the complete grammar in the form of separate and wholly independent and alphabetically arranged elements. This would give to any correspondent, even an unprepared one, of any nation, the immediate ability to understand your letter.
I finished university and began my medical career. Already I began to think about the publication of my project. I got ready the manuscript of my first pamphlet. (Dr. Esperanto. "An International Language. Introduction and Complete Vocabulary"), and began to look for a publisher. Here I met for first time the sad experience of life, the financial problem, with which I afterwards was obliged to battle strenuously. For two years I vainly sought a publisher. When I finally found one he kept me waiting six months in order to prepare the manuscript - and then refused. At last, after a great deal of trouble I was myself able to publish the pamphlet, in July of the year 1887. I was very excited before that time arrived. I felt that I stood at the Rubicon, and that from the day my book appeared there would be no possibility of retreat. I knew what fate awaited a physician who depends upon the public, when the public sees in him a follower of fantasies - a person who busies himself with mere hobbies. I felt that I was placing the whole happiness and welfare of myself and family upon the turn of a card. But I could not give up the idea which had entered my very blood - and I crossed the Rubicon.
