The Greek word ‘skepsis’, meaning ‘seeking’ and ‘skeptic’ is thus contrasted with dogmatic and in relation to some particular branch of science has reference to doubt as the truth of some assertation or supposed fact. The classic arguments for scepticism are that our senses are unreliable and that experts contradict each other.
Scepticism as a line of thought be be dated to Pyrrhon (365 – 275 BCE) and his school, although earlier roots might be inferred in the Sophists. Pyrrhon’s scepticism was essentially practically minded and aimed to imperturbability of mind. Scepticism was introdued into the Academy by Arcesilaus of Pitane (316 – 242 BCE) and formed the basis of Academic teaching until the headship of Antiochus (78 BCE).

A theory, hence, is built of reliable knowledge – built of scientific facts – and its purpose is to explain major natural processes or phenomena. Scientific theories attempt to explain nature by unifying many once-related facts or corroborated hypotheses. In the process of trying to establish reliable knowledge error must be considered.
Thus an important part of scientific method is to contrast, support, or cast doubt on a scientific theory. A theory in science is not a guess, speculation, or suggestion. A scientific theory is a unifying and self consistent explanation of fundamental natural processes or phenomena which is constructed of corroborated hypotheses.

Thus Arcesilaus, founder of the second or Middle Academy, with his sceptical attitude could claim to be following Socrates whose philosophical role could be said to refute error, rather than to impart knowledge. This attitude embodied itself in the practice of arguing for and against any given point of view without reaching any conclusions which led to a suspension of judgement.

In this way it might be said that the philosophical mode of scepticism deeply ingrained and affected the Academy and the whole future of academic endeavor. This reservation of conviction may be seen in the statistical agnosticism encountered where an idea proposed as an hypothesis accumulates empirical evidence and is indicated as increasingly reliable knowledge moving toward becoming a theory, model and law. The mode of skepticism might be expressed in this context as the reservation that no theory, model or law can be considered absolutely correct and is subject to new discoveries.
A key idea in science and critical thinking is cited as skepticism, which is commonly coined to refer to the constant questioning of ones beliefs and conclusions. Historically Scepticism is a reference to the doctrine of the Skeptics which expressed the opinion that real knowledge of any kind is unattainable and therefore judgement must be suspended.

Errors in experiments have several sources. There is error intrinsic to the instruments of measurement. Due to this type of error having equal probability of producing a measurement higher or lower numerically than the “true” value, it is referred to as random error.

In a field where there is active experimentation and open communication among members of the scientific community, the biases of individuals or groups may cancel out, because experimental tests are repeated by different scientists who may have different biases. In addition, different types of experimental setups have different sources of systematic errors. Over a period spanning a variety of experimental tests (usually at least several years), a consensus develops in the community as to which experimental results have stood the test of time.
A common mistake is to ignore or rule out data which do not support the hypothesis. The experimenter should be open to the possibility that the hypothesis is both, correct or incorrect. In the case where a scientist has a strong belief that a hypothesis is true or false, or may feel internal or external pressure to get a specific result there may be psychological tendency toward a bias which supports the scientist’s expectations. Incorrectly, data which do not agree with those expectations may not be checked as carefully.

Good scientists and critical thinkers constantly examine the evidence, arguments, and reasons for holding beliefs. Self-deception and deception of oneself by others are two common failings to the acquisition of reliable knowledge. An attempt to escape both deception by others and the far more common trait of self-deception is to repeatedly and rigorously examine the basis for holding ones beliefs.

Another mistake arises from the failure to estimate quantitatively systematic errors (and all errors). There are many examples of discoveries which were missed by experimenters whose data contained a new phenomenon, but who explained it away as a systematic background. Conversely, it could be said that there are many examples of alleged “new discoveries” which later proved to be due to systematic errors not accounted for by the “discoverers”.

Scientific method may be seen to attempt to minimize the influence of the scientist’s bias on the outcome of an experiment. That is, when testing an hypothesis or a theory, the scientist may have a preference for one outcome or another, and it is important that this preference not bias the results or their interpretation. The most fundamental error is to mistake the hypothesis for an explanation of a phenomenon, without performing experimental tests.
There is non-random or systematic error, due to factors which bias the result in one direction. No measurement, and therefore no experiment, can be perfectly precise. In science there is a standard way of estimating, and in some cases, reducing errors. Thus it is important to determine the accuracy of a particular measurement and, when stating quantitative results, to quote the measurement error. A measurement without a quoted error is relatively meaningless.
In the scientific process it is vital to question the truth and reliability of both the knowledge claims of others and the knowledge one already possesses. One way if doing this is to test beliefs against objective reality by predicting the consequences or logical outcomes of held beliefs and the actions that follow from these beliefs.

If the logical consequences of such beliefs match objective reality – as measured by empirical evidence – one can conclude that the beliefs are more greatly reliable knowledge than previously examined (that is, the beliefs have a higher probability of being true).