Etymologically, history comes from a Greek word that simply means information and research. That is, knowledge acquired through research. But this initial meaning has evolved to the current meaning, which refers to knowledge acquired through research regarding past events.

According to the RAE dictionary, history is the narration and exposition of past events worthy of memory, whether public or private, or also the discipline that studies and chronologically narrates past events.

On the other hand, historiography is the discipline that deals with the study of history, or also the bibliographic and critical study of the writings on history and their sources, and of the authors who have dealt with these matters. Finally, historiology is the theory of history and especially the one that studies the structure, laws or conditions of historical reality.

From our point of view, we will call history to the past events themselves, historiography to the study of past events, and historiology to the study of how history is studied.

The historical method is the set of procedures used by historians to investigate past events with primary sources and other evidence.

The historical method starts with the definition and delimitation of the subject of study, the formulation of the question or questions to be answered, the definition of the work plan, and the location and compilation of documentary sources, which are the raw material of the historian's work.

The next step is the analysis or critique of these sources. Within source criticism is external criticism, which is divided into major criticism and minor criticism, and internal criticism. Each one has specific characteristics.

External criticism has the function of avoiding the use of false sources. Therefore, it is a negative function. The part called major criticism, or also historical criticism or historical critical method, includes the dating of the source (the location in time), the location in space of the source, the authorship of the source, and the origin of the source. (the previous material from which it was produced). The part called minor criticism, or also textual criticism, looks at the integrity of the source (the original form in which it was produced).

Instead, internal criticism has the function of proposing how sources should be used. Therefore, it is a positive function. While external criticism is fixed on the form, internal criticism is fixed on the substance. Study the credibility, the probative value of the content.

After the analysis or criticism of sources, the last step of the historical method is the production of the final result, called historiographic synthesis. It consists of the formulation and establishment of interpretive hypotheses through the so-called historical reasoning.

For historians, milestones are historical events that cause very significant changes, that change the course of history, or the course of the historical phenomenon they affect but with consequences that are felt in different areas, in a chain effect.

There is no standard way to classify historical landmarks, but many different possibilities, and each historiographic school or each historian prioritizes some criteria or others. There is also no consensus classification in the popular books.

From our point of view, these are some of the possible qualifying criteria for historical milestones:

• Depending on whether it affects nature, human beings or what human beings do, and their interrelation
• By taxonomic categories of a domain
• By taxonomic categories of an economic activity
• By taxonomic categories of a profession
• By taxonomic categories of a discipline
• By level of transversality in areas, economic activities, economic sectors or professions
• By level of transversality in projects within fields, economic activities, economic sectors or professions
• According to the time in which they have happened (when)
• - By historical periods
• - By geological ages of the Earth
• - By seasons
• - For years
• - For months
• According to its protagonists (who)
• - By social class
• - By ethnic identity
• - By nationality
• - By gender identity
• - By age
• - By sexual identity
• - By trades / professions
• - By kinship ties
• According to the place (where)
• - By continents
• - By continental regions
• - By supranational regions
• - By countries
• - By geopolitical areas
• Depending on whether they are natural or artificial
• By level of innovation
• By level of influence
• By level of significance
• According to whether it is scientific or not
• By type of technology involved
• By type of techniques involved
• Depending on whether they have positive or negative consequences:
• - For the enviroment
• - For the population as a whole
• - For a specific social group
• - For the development of disciplines, areas, sectors or trades
• Depending on whether its consequences are short or long term (by level of longevity)
• According to the cause:
• - For the enviroment
• - For the population as a whole
• - For a specific social group
• - For the development of disciplines, areas, sectors or trades
• According to the rhythm of the changes they produce: abrupt or gradual

If the theoretical framework is chosen historical materialism, criteria are also possible:

• If it affects the infrastructure or structure
• When it affects infrastructure:
• - By type of production mode
• - By the forces of production affected
• - By type of raw materials
• - By type of technology used
• - By type of social relations of production
• If it affects the structure:
• - By type of ideology
• - By taxonomic categories of ideology

If the Sapiens methodology, based on systems theory

• If it affects the infrastructure or structure
• By systems
• By subsystems
• Depending on whether the milestone comes from outside the system or from within
• According to the function it fulfills within the system or subsystem
• According to the level of impact on the system

One of the possible criteria for classifying milestones is the level of influence or significance. More specifically, one way to classify historical milestones is according to whether they have caused paradigm shifts or not.

In his book The Structure of Scientific Revolutions, published in 1962, Thomas Kuhn argues that history is more than a succession or chronology of accumulated events, and that sometimes there are events that cause scientific revolutions and paradigm shifts.

For Kuhn, a scientific revolution is an episode of non-cumulative development, in which the old paradigm is totally or partially replaced by a new incompatible paradigm.

It can be compared with political revolutions, which also imply a moment of rupture between the old situation and the new situation, and therefore a replacement of an old situation by a new incompatible situation.

For Kuhn, paradigms are universally recognized scientific realizations that provide models of problems and solutions to a scientific community for a time. That is, the delimitation of a field of play and rules of the game.