When the legislator wishes to provide a milder or stricter criminal liability for a special subcategory of a certain category of punishable acts than for the rest of these acts, in addition to the basic type of a given offence (e.g. murder), the legislator will introduce a special (modified) type of the same offence, which corresponds to this subcategory (e.g. euthanasia). In comparison to the statutory description of the basic type of the offence, a statutory description of a special type of the offence contains an extra feature, which differentiates a given subcategory of acts from the rest of the category (a so-called modifying feature). Certain academics specializing in Polish criminal law, citing Władysław Wolter, adopt an inaccurate assumption, pursuant to which, as a result of introducing a special type of an offence, the statutory description of the basic type of this offence is automatically, by reason of logic, implicitly extended by the negation of the modifying feature. An inevitable consequence of this assumption, which is overlooked by its proponents, constitutes an unjustified narrowing of the scope of criminalization. The author argues that an even further narrowing of the scope of criminalization is led by significant errors, often made by followers of the assumption of implied negations of modifying features in the statutory descriptions of basic types of offences when implementing this assumption in the process of interpreting the criminal law provisions defining basic and special types of offences. He distinguishes and then discusses in detail three types of such errors and their consequences.