Bacon suggested systematic research in which all information on the topic was gathered and put into three tables:

1. Essence and presence
   In this table, all the instances in which the phenomenon was present need to be written down.
2. Deviation or absence in proximity
   In this table, all the instances similar to the ones in the first table in which the phenomenon was absent need to be written down.
3. Degrees of comparison
   In this table, all the instances in which the phenomenon was present in different degrees need to be written down.

Pragmatism has four methods of information gathering:

1. Method of tenacity
   This method includes the assumptions and beliefs people have because they have been around for a long time.
2. Method of authority
   This method includes knowledge which is formed by consulting authority.
3. A priori method
   This method includes using reason and logic to reach conclusions and this method includes deductive and intuitive knowledge.
4. Scientific method
   This method includes using the scientific method to obtain knowledge.

Science makes use of the correspondence theory of truth. Its claim of intellectual superiority is based on realism (1), objectivity (2), truth (3) and rationality (4). Postmodernism refers to a group of people who question the special status of science and see scientific explanations as stories told by scientists. They state that science is a social construction and that the truth of statements depends on how well they fit in with the paradigm rather than whether they represent reality.

Russell’s paradox demonstrates that the naïve set theory results in a contradiction, meaning that something is correct and false at the same time. Wittgenstein concludes that this paradox stems from a lack of clarity in what makes something meaningful. He makes several statements:

• The world is a totality of facts.
• Elementary facts are indivisible and independent of each other (i.e. logical atomism).
• Complex facts are a combination of elementary facts (i.e. constituents).
• A thought or statement expresses a possible state of affairs in the world.
• The state of affairs is the meaning of the thought.
• A thought is true if the state of affairs of the world occurs.
• Meaningful statements depict possible states of affairs.
• Meaningless statements depict impossible states of affairs.
• Language can only express a state of affairs.

It is possible that a thought is false but meaningful and language poses limitations on science as language cannot express anything other than a state of affairs (e.g. ethics are impossible). The focus of science on language is called the linguistic turn.

The Wiener Kreis sought demarcation criteria to distinguish science from pseudo-science and philosophical traditions. Wittgenstein’s meaningful sentences were used for this and this demoted philosophy to clarifying language and assessing whether sentences are meaningful.

Later, the Wiener Kreis used the verification principle as demarcation criterion and they made several points:

• Meaningful claims are empirical or logical.
• Logical claims are verifiable by looking at their form.
• Empirical claims are verifiable by using observation.
• Claims that are not verifiable are meaningless.

Sense data refers to factual descriptions of perception and the Wiener Kreis stated that experiences that are gained through sensory perception are neutral. The foundation of science is on the sense data as the Wiener Kreis focussed on certainty and precision and employs verification.

There are several problems with logical positivism:

1. The problem of separation of theory and observation
   It is not possible to separate theory and observation as theory cannot always be reduced to observation (e.g. intelligence).
2. The problem of theory-ladenness
   The theory and observation always influence each other as every observation is theory-laden.
3. The problem of underdetermination of theory
   Theories may be equal in their empirical consequences, meaning that the theories are underdetermined. In this case, it is not possible to choose the best theory and other criteria (e.g. elegance) are needed.
4. The induction problem
   It is not possible to verify general statements as it is not possible to observe everything.
5. The problem of unobservable entities
   The unobservable entities in theories cannot be verified nor reduced to observation, making it impossible to verify the theory.
6. The problem of observable entities
   It is not clear when an entity is observable as some entities require instruments to be observed.

It is unclear when an entity is unobservable as sometimes new instruments make a previously unobservable entity observable. Observation sentences refer to statements directly describing reality. They can be linked to each other and the theory using logic. They are attached using correspondence rules, meaning that theoretical sentences are reduced to observation.

Herschel stated that two different theories explaining the same phenomenon are okay as long as predictions can be made and tested to assess which theory is better. Schlick states that abstract concepts and theories are useful as long as they function as a summary of observations and meaningful statements.

Logical positivism (i.e. Wiener Kreis) comes to an end because sense data does not exist (1), everything is subject to interpretation (2), there are always multiple interpretations (3) and there is no certainty in the observation (4).

According to Popper, theories that can explain everything are flawed as they do not exclude events and do not make precise predictions. These theories are thus uninformative.

Popper has several important characteristics:

• Proposes that theories are bold conjectures whose predictions can be tested against observations (i.e. surpassing the need for theory-free observation)
• States that theories can make use of deduction to derive predictions about observations from the theories.
• Proposes falsification as a demarcation criterion.
• Introduces degrees of falsifiability; the more falsifiable a theory is, the better.
• Introduces the hypothetico-deductive model.

A more precise theory and a more general theory exclude more. The hypothetico-deductive model consists of several steps:

1. Observation
2. Constructing a theory based on observation.
3. Deduce predictions based on the theory.
4. Test the predictions using observation.
5. Evaluate the theory

Popper’s falsificationism is based on rationalism, although he believes that the ratio is fallible. This is called critical rationalism. Serendipity, the accidental discovery of something while looking for something else is not a problem for Popper.

Lakatos proposed nuanced falsificationism as direct falsification is very rare (1) and because researchers tend to stick to their theories (2). Researchers should switch theories if there is a better, non-falsified theory. Otherwise, revisions of the theory to fit anomalies instead of falsifying the entire theory are fine. The core of the theory cannot be revised. Revisions to the core of a theory are negative heuristics. Revisions to protect the core are positive heuristics.

Progressive research programmes are characterized by growth (1), new techniques (2) and more facts (3). Degenerative research programmes are characterized by shrinkage (1), no new techniques (2) and no increase in facts (3). Nuanced falsificationism states that researchers should stick with progressive research programmes and abandon degenerative research programmes.

The Quine-Duhem thesis states that a theory cannot be tested in isolation because everything depends on theory (e.g. instruments). Problems with falsification are that a falsification attempt can fail due to other factors than the theory (1), falsification also does not differentiate between better and less supported theories but only between refuted and not yet refuted theories (2) and researchers do not refute an entire theory based on one anomaly (3).

Kuhn proposed paradigm shifts, the shift from one general theoretical framework (i.e. paradigm) to another. A paradigm is a combination of theories, methodologies and is something the researchers are completely trained in which is all-encompassing and impossible to step out of.

A paradigm determines what is to be observed and scrutinized (1), which questions should be asked (2), how the questions are to be structured (3) and how the results of a scientific investigation should be interpreted (4).

Scientific progress occurs in several steps:

1. Pre-science
   This is a stage in which there is no paradigm.
2. Normal science
   This is a stage in which there is a paradigm and it is possible to conduct normal science.
3. Anomalies and crisis
   This is a stage in which there are anomalies which cannot be explained by the paradigm.
4. Revolution
   This is a stage in which there is a paradigm shift between two paradigms.
5. Normal science
   This is a stage in which there is a paradigm again and it is possible to conduct normal science. The crisis has been resolved.

Relativism states that there is no scientific progress because terms change meaning in theories between paradigms, meaning that the theories are not about the same thing anymore. This implies that a different paradigm leads to a different world view.

Feyerabend states that anything is permitted in science (i.e. “anything goes”) as he denies that methodological guidelines ensure progress in science.