There is no doubt that formalising information systems is of great value to an organisation. This enables, among others, business processes, rules, services and objects models to be standardized, structured, capitalized and reused. A formal information system involves a structured organisation, clearly defined roles and responsibilities and therefore a rational management. However, generalising a formalisation approach to all information system perspectives or all levels of granularity can inversely be fatal to the smooth running of the business, its management, and operation. The aim of this paper is to explore information systems formalinformal continuum, to discover and understand its characteristics, patterns, anti-patterns, and the forces partcipating to its equilibrium, and to propose recommendations to reach right level of formalisation *. * This work is partially financed by the research grant EvA (vulgarisation of Enterprise Architecture) n o 002/EN-SIAS/2011 of Université Mohammed V-Souissi. 1 To formalise is (i) to give (something) legal or formal status (a year has elapsed since the marriage was formalised), (ii) to give a definite structure or shape to (we became able to formalise our thoughts) (OUP, 2012). Formalisation for Husserl, is precisely the relationship of an object to form (Quesne, 2003). (Ostrom, 2009) distinguishes between rules-inform (dead letters) and rules-in-use (actually followed) (Kingston and Caballero, 2009). formalisation means a reduction in personal and relational elements of coordination and an emphasis on objectively documenting decisions, discussions, and work processes (Meijer, 2008). Human and Formalisation Example of implicit formalisation-man and bodily faculties externalisation. According to (Serres et al., 2004), what is a hammer else than a fist with a forearm, which fell to our arm. The technique was invented by outsourcing a bodily factulty. Actually, there exists a mechanism that produces continuous despecialisation of human organs. Human being is unique in his capacity to lose a faculty and to develop