A UNIFIED COMPLEXITY THEORY – ANNEX 0.0_ THE DEFINITION OF COMPLEX AND COMPLEXITY ©Ricardo Alvira. All rights reserved, with the exception of the photographs, retained by their authors. 6_ANNEXES A0.0_THE DEFINITION OF COMPLEX AND COMPLEXITY Currently the terms Complex and Complexity are used in many different fields, coexisting also very different definition proposals for both [sometimes even within the same field]. This is the first obstacle that must be solved for a Unified Theory, because defining a term [or ex‐ plaining the concept it refers to] is equivalent to setting the first premise 1 from which we infer the statements of the theory; different definitions equate to different premises and necessarily lead to different conclusions. Therefore, as the first step for the present theory, it is necessary to arrive at a definition of those terms which must have two qualities:  Be based on a sufficiently solid basis, which allows justifying the choice of such definition in‐ stead of others possible 2 .  Being able to embrace ‐and explain‐ the different utilizations of the term within the theories or fields of knowledge that are intended to 'unify'. All of them should be able to be concep‐ tualized as particular cases of the general definition. And we will be able to achieve it by reviewing the etymology of the two terms: A0.0.0_OF ‘COMPLEXUS’ AND ‘SIMPLEX’ The term 'complex' is incorporated to English language from the French complexe, which in turn adopts it from the Latin complexus, with the meaning of: "a surrounding, encompassing, encircling, embracing, embrace…” [Lewis, 1879] “embrace, link, chaining…” [Coromines y Pascual, 1996]. “union, link, chain, encircle, ...” [Segura, 2014] How has it evolved from the original meaning of complexus [mainly as "embrace"] to its different uses today? To understand it, we need to deepen both into the etymology of complexus and in its subsequent evolution. The term complexus is the past participle of complector which means: “to link, to embrace, to wrap, to surround...” [De Miguel, 1879] “to grasp, clasp, seize, encircle, surround, compass, enclose” [Lewis, 1879] “to embrace, to encompass, to grasp…” [Coromines y Pascual, 1996] 1 [Carnap, 1945, p.397] proposes that a definition is “an equivalence statement”. In certain way, it can be interpreted as the first ‘premise’ on which a theory is built. 2 Simply choosing one definition of the existing ones [or proposing a personal definition] would be an arbitrary act that may exclude from conclusions of the present text all those theories based on different definitions.