The Nature of Evidence

The Nature of Evidence

Common Definition:

1) A thing or set of things helpful in forming a conclusion or judgment (Free Dictionary)

2) That which tends to prove or disprove something; ground for belief; proof. (

3) Something, including testimony, documents and tangible objects that tends to prove or disprove the existence of an alleged facts (Black’s Law Dictionary)

4) My Definition: A thing or set of things offered up to another person intended to persuade them to form a new or different conclusion or judgment about a claim or strengthening the position of that claim.

General Types of Evidence

There are two general types of evidence used in both science and law – Physical and Testimonial evidence. Physical evidence is comprised of those forms of data that can be measured or quantified. Examples include fingerprints, accelerants, hair or fibers, etc. These types of evidence can be measured, weighed, and defined by a number of other physical methods. Testimonial evidence is comprised of observations either by the scientist or witnesses. Physical evidence or data is often called “real” evidence or “hard” data. The reason for this distinction is that physical evidence can be measured numerically while testimonial evidence is more subjective in nature. Each individual remembers events in a slightly different way and even observations of things like color depend on the individual’s visual ability to discern different hues. Another way to look at the two types of evidence or data is that physical evidence is objective and testimonial evidence is subjective.

Seen through another lens, there are two other ways to classify evidence: Empirical vs Historical Evidence: Evidence that is not directly observable in its original form, like fossils, archeological artifacts, or crime scene evidence. In order to analyze this type of evidence, a scientist must draw conclusions and make inferences about things they did not directly observe. This lies outside the realm of the scientific method and demonstrates that scientific study does have limits. Take, for example, a crime-scene investigator. When the crime-scene investigator arrives on a scene and collects evidence, they must use observational science to process the evidence (i.e., DNA and fingerprint analysis). They then have to apply the analysis to a criminal act that occurred in the past. This requires the interpretation of past events. Any scientific study that falls outside the boundaries of empirical, operational science falls into a distinct category we call historical science.

Philosophical Definition:

1) Evidence… is the kind of thing which can make a difference to what one is justified in believing or (what is often, but not always, taken to be the same thing) what it is reasonable for one to believe. (Stanford Encyclopedia of Philosophy)

2) For a short, easy to understand but clear and accurate video presentation on epistemology, argument and evidence, go to:


Science: knowledge or a system of knowledge covering general truths or the operation of general laws especially as obtained and tested through scientific method .

Scientific Method: principles and procedures for the systematic pursuit of knowledge involving the recognition and formulation of a problem, the collection of data through observation and experiment, and the formulation and testing of hypotheses

Science Fallacy: The philosopher Philip Sherrard has summed this up: “There is one particular fallacy from which we must free ourselves, and this is the idea that contemporary scientific theories are somehow neutral, or value-free, and do not presuppose the submission of the human mind to a set of assumptions or dogmas in the way that is said to be demanded by adherence to a religious faith. (The Guardian)

Scientific Evidence for Use in Legal Proceedings:

1) Scientific evidence is evidence culled from a scientific procedure that helps the trier of fact understand evidence or determine facts at issue in a judicial proceeding. (Free Dictionary)

2)“Adducing evidence” is the legal term for presenting or producing evidence in court for the purpose of establishing proof.) This meaning of evidence is reflected in the definitional section of the Indian Evidence Act (Stephen 1872: 149).[3] When lawyers use the term “evidence” in this way, they have in mind what epistemologists would think of as “objects of sensory evidence” (Haack 2004: 48). Evidence, in this sense, is divided conventionally into three main categories:[4] oral evidence (the testimony given in court by witnesses), documentary evidence (documents produced for inspection by the court), and “real evidence”; the first two are self-explanatory and the third captures things other than documents such as a knife allegedly used in committing a crime. (Stanford Encycolpedia of Philosophy)

3) In Escobedo the Court observed: “We have learned the lesson of history, ancient and modern, that a system of criminal law enforcement which comes to depend on the ‘confession’ will, in the long run, be less reliable and more subject to abuses than a system which depends on extrinsic evidence independently secured through skillful investigation” (Escobedo v. Illinois, 378 U.S. 478, 488–89 (1964)). (

4) “About one quarter of the citizens who had served on juries which were presented with scientific evidence believed that had such evidence been absent, they would have changed their verdicts—from guilty to not guilty” (Peterson et al., p. 1748).

5) A massive effort to test the validity of 100 psychology experiments finds that more than 50 percent of the studies fail to replicate. This is based on a new study published in the journal “Science.” (Hidden Brain)

6) Chain of Custody Problem – Proof of a chain of custody is required when the evidence that is sought to be introduced at trial is not unique or where the relevance of the evidence depends on its analysis after seizure. A proper chain of custody requires three types of testimony: (1) testimony that a piece of evidence is what it purports to be (for example, a litigant’s blood sample); (2) testimony of continuous possession by each individual who has had possession of the evidence from the time it is seized until the time it is presented in court; and (3) testimony by each person who has had possession that the particular piece of evidence remained in substantially the same condition from the moment one person took possession until the moment that person released the evidence into the custody of another (for example, testimony that the evidence was stored in a secure location where no one but the person in custody had access to it).

7) Problems with Scientific Evidence in Court:

a) In 2011, Adam Scott’s DNA matched with a sperm sample taken from a rape victim in Manchester—a city Scott, who lived more than 200 miles away, had never visited. Non-DNA evidence subsequently cleared Scott. The mixup was due to a careless mistake in the lab, in which a plate used to analyze Scott’s DNA from a minor incident was accidentally reused in the rape case.

b) Unfortunately, most forms of forensic evidence other than DNA have lacked similar scientific foundations. Instead, they have been characterized by much subjectivity, human observer bias, error and variability in processing and interpreting the evidence, lack of standardized procedures and accreditation programs in crime laboratories, inconsistent validation and unknown error rates, and, most worrisome, little incentive for conducting research into better, more reliable methods.

Scientific Evidence Not for Legal Purposes

1) Scientific evidence is evidence which serves to either support or counter a scientific theory or hypothesis. Such evidence is expected to be empirical evidence and in accordance with scientific method. Standards for scientific evidence vary according to the field of inquiry, but the strength of scientific evidence is generally based on the results of statistical analysis and the strength of scientific controls. (

2) Strength of Scientific Claims:

a) Predictive power, the power of a scientific theory to generate testable predictions

b) Explanatory power is the ability of a hypothesis or theory to explain the subject matter effectively to which it pertains. Its opposite is explanatory impotence.

3) Inference to the best explanation

In the past, various criteria or measures for explanatory power have been proposed. In particular, one hypothesis, theory, or explanation can be said to have more explanatory power than another about the same subject matter

  • if more facts or observations are accounted for;
  • if it changes more “surprising facts” into “a matter of course” (following Peirce);
  • if more details of causal relations are provided, leading to a high accuracy and precision of the description;
  • if it offers greater predictive power (if it offers more details about what should be expected to be seen and not seen);
  • if it depends less on authorities and more on observations;
  • if it makes fewer assumptions;
  • if it is more falsifiable (more testable by observation or experiment, according to Popper).

4)The types of evidence are listed from weakest to strongest.

Anecdotal & Expert Opinions

Anecdotal evidence is a person’s own personal experience or view, not necessarily representative of typical experiences. An expert’s standalone opinion, or that given in a written news article, are both considered weak forms of evidence without scientific studies to back them up.

Animal & Cell Studies (experimental)

Animal research can be useful, and can predict effects also seen in humans.
However, observed effects can also differ, so subsequent human trials are required
before a particular effect can be said to be seen in humans. Tests on isolated cells
can also produce different results to those in the body.

Case Reports & Case Series (observational)

A case report is a written record on a particular subject. Though low on the hierarchy of evidence, they can aid detection of new diseases, or side effects of treatments. A case series is similar, but tracks multiple subjects. Both types of study cannot prove causation, only correlation.

Case-Control Studies (observational)

Case-control studies are retrospective, involving two groups of subjects, one with a particular condition or symptom, and one without. They then track back to determine an attribute or exposure that could have caused this. Again, these studies show correlation, but it is hard to prove causation.

Cohort Studies (observational)

A cohort study is similar to a case-control study. It involves selection of a group of people sharing a certain characteristic or treatment (e.g. exposure to a chemical), and compares them over time to a group of people who do not have this characteristic or treatment, noting any difference in outcome.

Randomised Controlled Trials (experimental)

Subjects are randomly assigned to a test group, which receives the treatment, or a control group, which commonly receives a placebo. In ‘blind’ trials, participants do not know which group they are in; in ‘double blind’ trials, the experimenters do not know either. Blinding trials helps remove bias.

Systematic Review

Systematic reviews draw on multiple randomised controlled trials to draw their conclusions, and also take into consideration the quality of the studies included. Reviews can help mitigate bias in individual studies and give us a more complete picture, making them the best form of evidence.

Scientific Laws

Abel’s theoremAbel’s theorem allows us to evaluate many series in closed form. For example, when , we obtain for , by integrating the uniformly convergent geometric power series term by term on ; thus the series converges to by Abel’s theorem.Niels Henrik Abel
Ampère’s circuital law Ampère’s circuital law relates the integrated magnetic field around a closed loop to the electric current passing through the loop.André-Marie Ampère
Archimedes’s principleArchimedes’ principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluidArchimedes
Bernoulli’s principleBernoulli’s principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy.Daniel Bernoulli
Biot–Savart lawBiot–Savart law is an equation describing the magnetic field generated by a stationary electric current. It relates the magnetic field to the magnitude, direction, length, and proximity of the electric current. Jean Baptiste Biot and Félix Savart
Cayley–Hamilton theoremCayley–Hamilton theorem states that every square matrix over a commutative ring (such as the real or complex field) satisfies its own characteristic equation.Augustin Louis Cauchy
Coulomb’s lawCoulomb’s law, or Coulomb’s inverse-square law, is a law of physics for quantifying the amount of force with which stationary electrically charged particles repel or attract each other. Charles Augustin de Coulomb
Fermat’s principleFermat’s principle or the principle of least time, named after French mathematician Pierre de Fermat, is the principle that the path taken between two points by a ray of light is the path that can be traversed in the least time. This principle is sometimes taken as the definition of a ray of light.Pierre de Fermat
Gauss’s lawGauss’s law, also known as Gauss’s flux theorem, is a law relating the distribution of electric charge to the resulting electric field. The surface under consideration may be a closed one enclosing a volume such as a spherical surface.Johann Carl Friedrich Gauss
Graham’s lawGraham’s law of effusion (also called Graham’s law of diffusion) was formulated by Scottish physical chemist Thomas Graham in 1848. Graham found experimentally that the rate of effusion of a gas is inversely proportional to the square root of the mass of its particlesThomas Graham
Hilbert’s basis theoremHilbert’s basis theorem says that a polynomial ring over a Noetherian ring is Noetherian.David Hilbert
Lagrange’s theoremLagrange’s theorem, in the mathematics of group theory, states that for any finite group G, the order (number of elements) of every subgroup H of G divides the order of G.
Le Chatelier’s principleLe Chatelier′s Principle is the principle when a stress is applied to a chemical system at equilibrium, the equilibrium will shift to relieve the stress. In other words, it can be used to predict the direction of a chemical reaction in response to a change in conditions of temperature, concentration, volume, or pressure.Henri Louis le Chatelier
Maxwell’s equationsMaxwell’s equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits.James Clerk Maxwell
Newton’s law of universal gravitationthe law states that every point mass attracts every other point mass by a force acting along the line intersecting both points. The force is proportional to the product of the two masses, and inversely proportional to the square of the distance between them.
Newton’s laws of motionFirst law: In an inertial frame of reference, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force.
Second law: In an inertial reference frame, the vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma.
Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.
Ohm’s lawOhm’s law states that the current through a conductor between two points is directly proportional to the voltage across the two points.Georg Ohm
Pascal’s lawPascal’s law or the principle of transmission of fluid-pressure is a principle in fluid mechanics that states that a pressure change occurring anywhere in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere.Blaise Pascal
Pythagorean theoremIn mathematics, the Pythagorean theorem, also known as Pythagoras’ theorem, is a fundamental relation in Euclidean geometry among the three sides of a right triangle. It states that the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides.Pythagoras
Rolle’s theoremRolle’s theorem states that for any continuous, differentiable function that has two equal values at two distinct points, the function must have a point on the function where the first derivative is zero.Michel Rolle
Stokes’s lawStokes’s law, for the frictional force – also called drag force – exerted on spherical objects with very small Reynolds numbers in a viscous fluid. Stokes’s law is derived by solving the Stokes flow limit for
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