O presente trabalho se estrutura em torno da resposta a duas questões: O que é uma decisão motivada? e Quais as consequências de uma decisão imotivada?. Nesta perspectiva, partese da definição da motivação como um discurso cuja função é a de justificar racionalmente a decisão judicial. Esta justificativa racional tem funções endoprocessuais e extraprocessuais. Dentre as funções extraprocessuais, destaca-se a de conferir legitimidade à atuação jurisdicional no Estado Democrático de Direito. Ainda no âmbito da norma constitucional que impõe ao juiz o dever de fundamentar suas decisões, demonstra-se que ela se estrutura sob a forma de regra, nos termos da teoria dos princípios de ALEXY, com a consequência de que os limites para a caracterização de uma decisão como motivada são rígidos. Passa-se, então, à construção de um modelo teórico de estrutura da motivação sob a ótica funcional. Na construção desse modelo, demonstra-se que a estrutura e conteúdo da motivação no caso concreto dependem da interação de um modelo mínimo de justificação adequada, um modelo intermediário delimitado pelo contraditório e um limite máximo delimitado pela linguagem. A partir desse modelo interativo exploram-se as consequências dos vícios de motivação segundo uma teoria das nulidades dos atos processuais e, assim, conclui-se que a motivação só será considerada inexistente em caso de omissão gráfica e que qualquer vício de fundamentação é uma atipicidade relevante que deve ser nulificada. / The present work is structured around answering two questions: \"What is a motivated decision?\" and \"What are the consequences of an unjustified decision?. In this perspective, we start from the definition of motivation as a speech whose function is to rationally justify the decision. This rational justification has legal and constitutional functions. Among the constitutional functions one that stands out is to legitimate the courts role under in the rule of law. Also as part of the constitutional rule determining courts to motivate their decisions, it is shown that it is structured in the form of a rule in accordance with the principles theory of ALEXY, resulting that the limits for the characterization of a motivated decision are rigid. Then it is possible to create a theoretical model of the structure of motivation from a functional perspective. When building this model, we demonstrate that the structure and content of motivation depends on the interaction of a minimal model of proper justification, an intermediate model bounded by the adversarial principle, and another model, bigger than the others, defined by the language. From this interactive model it becomes possible to explore he consequences of the defects of motivation according to a nullity of procedural acts theory and thus it is concluded that motivation wont be considered existent only in case of graphical omission and that any defective reasoning must be nullified.

Le 21ème siècle est marqué par une évolution technologique et scientifique de très haut niveau qui permet d'accomplir toutes les investigations techniques et scientifiques pour tous les domaines de la science. Les Magistrats ont recours, dans le cadre des investigations nécessaires à la manifestation de la vérité, à des hommes de l'art. L'expert judiciaire algérien, comme toute autre expert, obéit aux principes universels inhérents à la protection et sauvegarde des libertés fondamentales et surtout à l'éthique. L'expertise, quant à elle, doit impérativement obéir aux lois et règlements qui nous gouvernent dont le résultat obtenu ne doit souffrir d'aucune irrégularité et doit être opposable aux tiers pour emporter la conviction des juges. / The 21st century is marked by a very high level of technological improvements and scientific, allowing to perform all technical and scientific investigations in all science's areas. The judges are used, in the context of investigations necessary for the truth's manifestation to art's men. Algérian judicial expert, like any other expert, obeys universal principles inherent in the protection and safeguarding of fundamental freedoms and especially ethics. Expertise, about it, must imperatively obey the laws and regulations who govern us that the result should not suffer any irregularity and shall be binding on third parties to carry conviction of judges.

Cette thèse a pour objectif d’étudier les mécanismes par lesquels des expertises judiciaires sont conduites dans lecadre d’un procès afin d’assurer une recherche d’information préalable à la prise de décision du juge. Nous analysonsl’efficacité du recours à des mesures d’expertise en nous basant sur deux critères : le coût que les expertises font pesersur le système judiciaire et l’impact des expertises sur la qualité de la prise de décision du juge. Les travaux réalisésse divisent en quatre grands thèmes.Premièrement, nous étudions les incitations de l’expert judiciaire et nous mettons en évidence l’existence de problèmesd’aléa moral et de sélection adverse dans la relation qu’entretiennent le juge et l’expert. Deuxièmement, nous offronsune vue comparative de deux grandes catégories de procédures dans le contexte desquelles une expertise peut êtredemandée : la procédure inquisitoire et la procédure accusatoire. Notre objectif est de déterminer quelle procédureest préférable, compte tenu des deux critères d’évaluation de l’expertise judiciaire que nous avons précédemmentcités. Troisièmement, nous étudions spécifiquement le problème d’aléa moral existant dans la relation qui lie l’expertau juge, cette relation s’articulant autour du travail de recherche réalisé par le premier et du contrôle exercé par lesecond. Quatrièmement, nous mettons en évidence que des conflits d’intérêts de la part de l’expert, ou l’utilisationd’une méthodologie biaisée dans la conduite de ses travaux d’expertise, peuvent entraîner des erreurs dans la prise dedécision. Dans ce contexte, nous tentons de déterminer dans quelle mesure la présence d’un mécanisme d’appel peutpermettre de réduire les effets pervers d’un potentiel biais dans les résultats de l’expertise. / The objective of this thesis is to study the mechanisms by which an expert, who is appointed by the judge or by aparty to search evidence, may contribute to increase the quality of the judicial decision-making. We use two criteriato study how the use of experts may benefit to the judicial decision-making : the cost of expertise and the cost oferrors due to incorrect decisions by the judge. Our work is divided into four chapters.Firstly, we study the judicial expert’s incentives and we highlight the existence of moral hazard and adverse selectionproblems in the relationship between the judge and the expert. Secondly, we offer a comparative view of two differentcategories of procedure in which experts may be appointed : the inquisitorial procedure and the adversarial procedure.Thirdly, we study more specifically the relationship between the judge and the expert, when the judge exerts a controleffort and the expert exerts a research effort. Finally, we highlight the consequences of potential conflicts of interestsfrom the expert, or the consequences of a bias in the methodology used to conduct the expertise. Such conflicts ofinterests or bias may create some errors in the decision-making. In this context, we investigate how the presence ofan appeal mechanism may reduce the adverse effects of a potential bias in the results of the expertise.