(source) 
PierreSimon Laplace
(23 Mar 1749  5 Mar 1827)

PierreSimon Laplace Quotes on Ignorance (5 quotes)
>> Click for 32 Science Quotes by PierreSimon Laplace
>> Click for PierreSimon Laplace Quotes on  Analysis  Biography  Cause  Chance  Knowledge  Law  Mathematics  Nature  Observation  Phenomenon  Probability  Theory 
>> Click for 32 Science Quotes by PierreSimon Laplace
>> Click for PierreSimon Laplace Quotes on  Analysis  Biography  Cause  Chance  Knowledge  Law  Mathematics  Nature  Observation  Phenomenon  Probability  Theory 
The present state of the system of nature is evidently a consequence of what it was in the preceding moment, and if we conceive of an intelligence that at a given instant comprehends all the relations of the entities of this universe, it could state the respective position, motions, and general affects of all these entities at any time in the past or future. Physical astronomy, the branch of knowledge that does the greatest honor to the human mind, gives us an idea, albeit imperfect, of what such an intelligence would be. The simplicity of the law by which the celestial bodies move, and the relations of their masses and distances, permit analysis to follow their motions up to a certain point; and in order to determine the state of the system of these great bodies in past or future centuries, it suffices for the mathematician that their position and their velocity be given by observation for any moment in time. Man owes that advantage to the power of the instrument he employs, and to the small number of relations that it embraces in its calculations. But ignorance of the different causes involved in the production of events, as well as their complexity, taken together with the imperfection of analysis, prevents our reaching the same certainty about the vast majority of phenomena. Thus there are things that are uncertain for us, things more or less probable, and we seek to compensate for the impossibility of knowing them by determining their different degrees of likelihood. So it was that we owe to the weakness of the human mind one of the most delicate and ingenious of mathematical theories, the science of chance or probability.
— PierreSimon Laplace
The word 'chance' then expresses only our ignorance of the causes of the phenomena that we observe to occur and to succeed one another in no apparent order. Probability is relative in part to this ignorance, and in part to our knowledge.
— PierreSimon Laplace
What we know here is very little, but what we are ignorant of is immense
— PierreSimon Laplace
Without any doubt, the regularity which astronomy shows us in the movements of the comets takes place in all phenomena. The trajectory of a simple molecule of air or vapour is regulated in a manner as certain as that of the planetary orbits; the only difference between them is that which is contributed by our ignorance. Probability is relative in part to this ignorance, and in part to our knowledge.
— PierreSimon Laplace
[Science] dissipates errors born of ignorance about our true relations with nature, errors the more damaging in that the social order should rest only on those relations. TRUTH! JUSTICE! Those are the immutable laws. Let us banish the dangerous maxim that it is sometimes useful to depart from them and to deceive or enslave mankind to assure its happiness.
— PierreSimon Laplace
See also:
 23 Mar  short biography, births, deaths and events on date of Laplace's birth.
 PierreSimon Laplace, 17491827, by Charles Coulston Gillispie.  book suggestion.