An expert witness is a person permitted by a judge to give opinions at trial. Most witnesses are usually only permitted to testify only about facts – what they saw or heard or otherwise have personal knowledge of. (There are certain exceptions to this rule.)
But experts have specialized knowledge, training or experience and thus have the right to give an opinion about some issue in a case. The judge determines whether a person who is offered to give expert testimony has the qualifications to be recognized as an expert, and the jury determines what weight to give to the expert’s testimony.
For example, in a Tennessee medical malpractice case expert testimony is almost always necessary to prove that the health care provider did not comply with the recognized standard of professional practice in the community where the patient was injured (or in similar communities) and that the injury (or death) occurred as a result of that error. The patient’s lawyer has the responsibility to locate and employ a qualified expert and the judge has the responsibility to ensure that the expert is qualified to give an opinion. The failure of a patient to have a proper expert in a medical malpractice case will almost always result in a loss of the case. (There are very rare exceptions to this rule. Only an experienced Tennessee medical malpractice attorney will understand exactly when it is possible to avoid the use of an expert witness on one or more issues in a medical malpractice case.)
Tennessee Injury Law Center

