There are three principal means of acquiring knowledge available to us: observation of nature, reflection, and experimentation. Observation collects … - Denis Diderot

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There are three principal means of acquiring knowledge available to us: observation of nature, reflection, and experimentation. Observation collects facts; reflection combines them; experimentation verifies the result of that combination. Our observation of nature must be diligent, our reflection profound, and our experiments exact. We rarely see these three means combined; and for this reason, creative geniuses are not common.