Heart of Darkness was written between the dates of 1898 and 1899, when Joseph Conrad was able to overcome his lack of inspiration and found his appropriate way of writing. Conrad himself admitted it took a lot of effort for him to write this novel, although we know about the great capacity of this author. He had been trying to work on his novel The Rescue for a year (a novel that he was not able to finish until his last days), and in the summer of 1898 he started writing Youth, which was published in 1902 at the same time that Heart of Darkness and The End of the Tether.
         If we pay attention to Youth, we will find that in this book it is the first time where we can find a character of great importance that Conrad will use in some of his subsequent novels: Marlow, a captain of an English ship that Conrad will use to tell his personal story. Marlow can be considered a very special character, and is the one on whose shoulders falls various variable performances.
         Conrad uses this character to introduce a new way of writing, which is the narration within narration. This is a technique which allows the author to stay apart, not to get into the story and to pepper the narration with some  comments of his own life, normally untimely ones. But we can not consider Marlow as just one more character. Marlow is a sailor, but there is no relation between Marlow and the sailors in The Nigger of the "Narcissus" or in Typhoon. These people are common people, with the vices and virtues that Conrad had known well among the people that sailed with him. They are generic beings, representing the class of the merchant seamen, with the virtues that Conrad saw in them: integrity and courage; and the weaknesses of the sailors he knew. But we can’t find this in the character of Marlow. Marlow as a narrator doesn’t look as a human character, but he seems to represent a moral attitude: the attitude of Conrad himself. As a way of presenting events, the character of Marlow is very useful because of the realism that he is able to give from his perspective of the main character and also as a commentator. From this last perspective, the opinions he expresses give the story a particular meaning. Conrad relive events of his own life, and with the character of Marlow he obtains two different effects: he presents the action with  authenticity and immediacy and at the same time he also extends and classify them from the distance there is between them and Conrad himself.
         Nevertheless, the moral attitude of Marlow has also ambiguities, and his conclusions usually has the sense of doubts: the doubts that Conrad always had. The interruptions in the narration of Marlow have also a double finality: when the emotions are too intense to be expressed, Marlow stops the story and he comes back for a moment, with his companions to comment something marginal or even to ask them. These short interruptions make the action more realistic and fluid. Furthermore, sometimes Conrad uses them to avoid the necessity of concluding a comment, showing with this his ambiguity.
         We can deduce that Joseph Conrad felt very comfortable with the character of Marlow, given that in a very short period of time he wrote three important novels where  this character appeared.
         Heart of Darkness is a long story about the experience in the Congo, but also a complex study of human emotions. It is, like most of Conrad’s works a semi-autobiographic book. Therefore we can find lots of links between this work and Conrad’s  life. In this novel Conrad explains the subjects that always obsessed him: the problem of human solitude and the internal struggle between man and the uncontrollable power of the nature.
         An Outpost of Progress is, with Heart of Darkness the only one novel that Conrad wrote about the Congo, and it is the first time he expresses his own feelings about Africa. The episode that Conrad tells through the impressions of  Marlow is, referring to his structure, very simple. We can consider this as the report of the voyage of  Marlow, through the river Congo to relieve a sales representative who is seriously ill. But are the characters who receive and express most part of the strength of the moral reflection.
         Conrad is worried about the human solitude, and he testes the character with isolation. Marlow, who is still aware of his distant relationship with  the wildness of this original place, doesn’t succumb to the strength of the darkness. He represents  the city life and the power of the tradition and the social ties. But the scepticism of Conrad is not complete; Marlow, who is practically his representation in this story, keeps alive  his integrity until the end. The strength of the jungle have not been able to overcome Marlow. Nevertheless , the process in Kurtz is very different. He is not a trader as the other; he has not been a part of this mean world. He is alone like Marlow , and he just have to confront the jungle. The only difference between Marlow and Kurtz is that the second one  lacks of self-control, his heart is hollow. The fact of being alone with nature in primitive state, the lack of social pressure, will end up dominating this man who is not able to control his own instincts. This effect will make him discover the mysterious truth, which talks about whispers, which make him feel that now he is able to recognise the reality, the hidden truth. Because of his lack of self-control, he lets the wild instincts of the jungle get the better of him, this instincts that the jungle arouse. Only in the end of his life, Kurtz will express the terrible feeling when he discovers the spell that has been coming over him: "A feeling of horror".
         Despite all his personal doubts, Marlow manages to meet Kurtz, but he suffers a partial defeat. When Marlow arrives, he does not really find Kurtz, but the jungle, with all his mystery expressed through Kurtz, who is the combination of the darkness in the jungle and the inner darkness of the human being. But Marlow has to pay a very high price for the revelation he now knows, which is represented by the final lie about the memory of Kurtz. Nobody can escape from the subtle influences of the darkness. Nobody except from the pilgrims who seem not to have capacity enough to break his inscrutable universe. They live in a micro-world that they have created, full of falseness, hypocrisy,  blinded by ambition but without any moral value.
         Conrad’s art uses the description, almost as an exclusive way to let us get into this world of nightmares (hallucinations more than bad dreams), where Heart of Darkness takes place. Is Marlow who through his own feelings, is setting the environment (terribly aggressive) where the clash between him and Kurtz will take place, which is the high point of this experience. Talking about the narrative technique of Conrad it is important to bear in mind his aspirations brilliantly summarised in the preface that he wrote for the edition of 1898 in The Nigger of the "Narcissus".
          From the first pages, Conrad introduces the reader to the world of darkness in the description at the beginning of the book. Heart of Darkness is a Conrad’s novel in which he constantly plays with light effects, which is one of the most effective elements of Conrad narrative technique. Thus, Conrad creates an oppressive atmosphere of extreme sensuality where everything seems to be catch in a spider’s web of an immense and continuous jungle, which begins and ends in the mouth of the Thames. Therefore in this book there is not any beginning nor end, because the end is just the return to the beginning, to the Londoner night and also to the origin of the civilisation. We can also find a constant obsession shown in all this work which is the civilised man in search of the limits of his nature.
         The symbolism in this book does not widely differ from the symbolism in other  works of Conrad works, and it’s quite naive. But his use is perfectly balanced with a series of descriptions that, beginning with the disembark of Marlow in the Central Station, goes to the arrival to the Interior Station in a crescendo, which reaches the crucial moment in the goodbye of Kurtz. We also can see this element in the rhythm of the narration but also through some optic effects very interesting that Conrad uses brilliantly. We can choose as an example of this, the character of Kurtz, which is the most enigmatic and original character of this work.
         Conrad’s narrative technique is not perfect, and the degree of psychological investigation in each of the character of Heart of Darkness is only outlined. Nevertheless, though Conrad is maybe too influenced by his Slavic temperament, we can find here the first elements which he will use for the creation of a new universe. This universe, though is not very large, will be enough to show a series of antagonistic moral attitudes where Conrad expresses his own very peculiar philosophy.