Case Name: ESTATE OF O'KEEFE
Court: Probate Court of the City and County of San Francisco
Jurisdiction: California
Decision Date: 1878-01
Citations: 1 Myrick 154
Docket Number: 
Parties: ESTATE OF O’KEEFE.
Judges: 
Reporter: Reports of Cases in the Probate Court of the City and County of San Francisco, from January 1, 1872, to December 31, 1879, Milton H. Myrick, Probate Judge
Volume: 1
Pages: 154–155

Head Matter:
ESTATE OF O’KEEFE.
January, 1878.
Will.—Mental incapacity abising feom alcoholism:.—Experts, Opinions of.— Charge to jury.
The opinions of medical experts as to the condition of a given man’s mind are often unsatisfactory. The opinions are to be received with distrust and many allowances, for the reason that, while an expert in exact sciences or in mechanics has tangible or ascertainable facts whereon to base liis opinion, those scientists who profess to understand the quality or emotions of the human mind have, in great part, to rely upon mere conjectures for their inductions, which inductions are often warped or fitted to pet theories or prejudices.
Santa Clara County, Probate Court,
M. H. Myrick, presiding.
D. M. Delmas and Hall McAllister, for proponents.
F. A. Spencer, for contestants.

Opinion:
The contest was made on the ground of unsoundness of mind, the result of long continued intoxication. Various medical witnesses were examined upon either side; hypothetical questions were put to them, and replies were received. Referring to the testimony of these experts, the Court instructed the jury:
The testimony of experts is frequently unsatisfactory and many times unreliable. It is unsatisfactory because it cannot convey to our minds the precise reasons why the conclusions are reached; and it is unreliable because it is frequently based upon speculation instead of facts. Experts in the exact sciences and in mechanics, who base their opinions upon the laws of nature and of the exact sciences and their own experience with those laws, have tangible facts before them; but where the opinions are based upon speculation, where the subject of the inquiry, viz: the operation and condition of the human mind, is beyond the possibility of human knowledge, we should receive those opinions as at least uncertain. So, when we see a person perform such or such an act, we can form an opinion whether the act is rational or irrational, whether it is consistent with the standard of average human intelligence and reasonableness; but when we advance to speculations upon what would or not follow upon some supposed existence of mental condition, we go beyond the scope of knowledge and tread upon the realms of imagination or conjecture.
You are instructed, therefore, that while we receive, and you will take into consideration, the opinions of experts, such opinions are not entitled to as much weight as facts, especially where there is a conflict between an opinion and a fact. When a fact is established, it is a fact, and cannot be overcome; while an opinion is but an opinion, and may be true and it may be untrue. Opinions of different experts are often diametrically opposed to each other, even when based upon the same supposed condition of things.