There are three principal means of acquiring knowledge... observation of nature, reflection, and experimentation. Observation collects facts; reflection combines them; experimentation verifies the result of that combination.
Denis Diderot

There is a wisdom in this beyond the rules of physic: a man's own observation what he finds good of and what he finds hurt of is the best physic to preserve health.
Francis Bacon

There is no better proof of a man's being truly good than his desiring to be constantly under the observation of good men.
Francois de La Rochefoucauld

There is no more difficult art to acquire than the art of observation, and for some men it is quite as difficult to record an observation in brief and plain language.
William Osler

There's certainly nothing original about the observation that conscious experience poses a hard problem.
David Chalmers

Therefore, the observation must be explicitly made: In the Middle East and in the Muslim world, suspicions linger concerning the objectives of the West and notably the US.
Recep Tayyip Erdogan

Those who have heard me speak from time to time know that quite often I cite the observation of that great American author, Mark Twain, who said, history does not repeat itself, but it rhymes.
J. D. Hayworth

To me, photography is an art of observation. It's about finding something interesting in an ordinary place... I've found it has little to do with the things you see and everything to do with the way you see them.
Elliott Erwitt

We are told that the first part of the process is to select the very smallest seeds from the smallest plants, which is not at all unlikely, but I cannot speak to the fact from my own observation.
Robert Fortune

We cannot create observers by saying 'observe,' but by giving them the power and the means for this observation and these means are procured through education of the senses.
Maria Montessori

We have seen that no religion stands on the basis of things known; none bounds its horizon within the field of human observation; and, therefore, as it can never present us with indisputable facts, so must it ever be at once a source of error and contention.
Francis Wright

We learn this by the precepts that Jesus left. He observed that the people were looking outward, and assured them that the kingdom of God cometh not with outward observation; and for this reason, that it was only to be known in man.
Elias Hicks

We may take it to be the accepted idea that the Mosaic books were not handed down to us for our instruction in scientific knowledge, and that it is our duty to ground our scientific beliefs upon observation and inference, unmixed with considerations of a different order.
Asa Gray

Where conscious subjectivity is concerned, there is no distinction between the observation and the thing observed.
John Searle

Where observation is concerned, chance favors only the prepared mind.
Louis Pasteur

Wisdom and understanding can only become the possession of individual men by travelling the old road of observation, attention, perseverance, and industry.
Samuel Smiles

Women are always most observed when they seem themselves least to observe, or to lay out for observation.
Samuel Richardson