This dissertation concerns an empirical research focused on observing the case law of the Appellate Court of Justice of Minas Gerais, Brazil, about sanctioning young offenders. I identify socially available ideas, senses, and thoughts that become incorporated as standard-settings to the discourse of State Appellate judges. The online empirical data (www.tjmg.jus.br). covers a period from 03.08.2010 until 01.12.2016, composed of approximately one thousand decisions. Keywords connected to the juridical language routinely employed in young offenders' records guided the further process of gathering seventy-seven sampling dossiers. The decisions herein studied typically contain summaries of main reasons and judicially assessed evidence to prove the accusation; and also rationales, reasoning patterns, beliefs, and other motives the judges consider to ruling the concrete case. Therefore, the research places particular emphasis on describing, characterizing, and understanding the influences of many idea systems and, in addition, of the current way of thinking the Adult Criminal Law Justice in the Juvenile Criminal Justice decisions. So, the research question is: "How have Appellate judges mobilized socio-legal semantics and idea systems to make sense of criminal sanctions imposed on young offenders?" This research adopted the theory of Modern Penal Rationality to characterize one of the idea systems identified in this investigation and construct some elements of its knowledge problem that address the epistemological obstacles to the evolution of the juvenile criminal justice subsystem in criminal matters. Due to my professional background and empirical observations of some dossiers, I contend that at least three idea systems influence the Appellate judges' decisions, in the social context of the Juvenile Criminal Law subsystem, as follows: 1) "Modern Penal Rationality" (as described by Pires and conceived for adults in the criminal justice system); 2) "Doctrine of Irregular Situation" (as provided by the revoked Brazilian "Code of Minors"); and 3) "Doctrine of Integral Protection" (as established in the 1988 Brazilian Constitution and in the 1990 Child and Adolescent Statute). Thus, the analysis shows how the decision-making process by the Court of Appeal - trying to proceed with an accommodation account of presumably conflicting values - selects idea systems linked to old theories of punishment to shape the logical structure of juvenile sanctions. I demonstrate that "common legal sense" and "taken for granted" statements apply to induce "severe" sanctions imposed without considering the specificity of the case by the rules of Juvenile Criminal Justice. As a result, I reveal that punitive reasoning prevails in juvenile delinquency judgments rather than child and youth protection, and I also describe the social-legal practice of the language of Juvenile Criminal Law in the Court of Appeal's environment.