Logic is that branch of normative science which studies the conditions of truth, or that kind of excellence which may or may not belong to objects considered as representing real objects.
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…logic, as a normative science, entirely disregards what the particular state of things may be, and undertakes [to] show what procedure must lead to the discovery of truth, whatever that truth may be.
http://www.commens.org/dictionary/entry/quote-reasons-conscience-practical-treatise-theory-discovery-wherein-logic-15