understanding (ˌʌndəˈstændɪŋ) n 1. the ability to learn, judge, make decisions, etc; intelligence or sense 2. personal opinion or interpretation of a subject: my understanding of your predicament. 3. a mutual agreement or compact, esp an informal or private one 4. chiefly Brit an unofficial engagement to be married 5. (Philosophy) philosophy archaic the mind, esp the faculty of reason 6. on the understanding that with the condition that; providing adj 7. sympathetic, tolerant, or wise towards people 8. possessing judgment and intelligence ˌunderˈstandingly adv Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014 log·ic (lŏj′ĭk) n. 1. The study of principles of reasoning, especially of the structure of propositions as distinguished from their content,and of method and validity in deductive reasoning. 2. a. A system of reasoning: Aristotle's logic. b. A mode of reasoning: By that logic, we should sell the company tomorrow. c. The formal, guiding principles of a discipline, school, or science. 3. Valid reasoning: Your paper lacks the logic to prove your thesis. 4. The relationship between elements and between an element and the whole in a set of objects, individuals,principles, or events: There's a certain logic to the motion of rush-hour traffic. 5. Computers a. The nonarithmetic operations performed by a computer, such as sorting, comparing, and matching, thatinvolve yes-no decisions. b. Computer circuitry. c. Graphic representation of computer circuitry. rea·son (rē′zən) n. 1. a. The basis or motive for an action, decision, or conviction: There are good reasons to learn a foreignlanguage. See Usage Notes at because, why. b. A declaration made to explain or justify action, decision, or conviction: What reasons did she give for leaving? c. A fact or cause that explains why something exists or has occurred: The reason for the building's collapse isunknown. d. Logic A premise, usually the minor premise, of an argument. 2. a. The capacity for logical, rational, and analytic thought; intelligence: "Most of us would like to believe thatwhen we say something is right or wrong, we are using our powers of reason alone" (Carl Zimmer). b. The limit of what is reasonable: "It is a curious thing that, when a man hates or loves beyond reason, he isready to go beyond reason to gratify his feelings" (Rudyard Kipling). c. A normal mental state; sanity: He has lost his reason. v. rea·soned, rea·son·ing, rea·sons v.tr. 1. To determine or conclude by logical thinking: The doctor reasoned that the patient had a virus. 2. To persuade or dissuade (someone) with reasons: "You boast ... of having reasoned him out of his absurd romance"(William Makepeace Thackeray). v.intr. 1. To use the faculty of reason; think logically: What would lead you to reason so? 2. To talk or argue logically and persuasively: tried to reason with her son to eat a good breakfast. 3. Obsolete To engage in conversation or discussion. Idioms: by reason of Because of. in reason With good sense or justification; reasonably. within reason Within the bounds of good sense or practicality. with reason With good cause; justifiably. [Middle English resoun, from Old French raison, from Latin ratiō, ratiōn-, from ratus, past participle of rērī, toconsider, think; see ar- in Indo-European roots.] rea′son·er n. Synonyms: reason, intuition, understanding, judgment These nouns refer to the intellectual faculty by which humans seek or attain knowledge or truth. Reason is the power to think rationally and logically and to draw inferences: Intuition is perception or comprehension, as of truths or facts, without the use of the rational process: Understanding is the faculty by which one understands,often together with the resulting comprehension Judgment is the ability to assess situations or circumstances and draw sound conclusions: I lead into this post with the dictionary definitions of these terms knowing full well that such definition is irrelevant with many social groups today as they see context as more important than defined meaning today. For such people all I can say is that you are endorsing the fragmentation of the language into a hodgepodge of confusion and meaninglessness. For all the rest of you; these three words Logic, Reason, and Understanding are subsets of one another that pertain to how we come to an operable understanding of the world around us, and they can still be abused for other purposes, but understanding Reality is still their most predominate uses. We operate in the real world by what we understand it to be like. As we lose this confidence in our understanding of the world, we can slide into various mental problems, as it is such a basic function of our minds to assemble what we know into a model of what we think of as a close semblance of the Reality around us. I am not confident this is true as one can read through history and find world views of many societies that were sadly off from Reality in many ways. And each of them thought their model of Reality to be as firm and useful as our own; what surprises lie in store for us? The use of Reason is one tool we use to model our understanding of Reality and can even make us aware that modeling Reality is all we are really doing. We are grasping through the darkness through gossamer veils that obscure and cloud each thing we touch. How do we know what is Real, what is imaginary/frightful and what is True? We use reason to sort out the whimsical, from the frightful, from the concrete. It comes in many forms, for example a discussion I am having with a friend about the rate of fire of musket units during the Napoleonic Wars. He thinks it was a maximum of four volleys a minute and yet the exceptional crack units were capable of five which the Prussians and Brits had mastered for most of their musketmen. We use historical reports, expert opinion and hopefully clear thinking mixed in with bombast and frivolous jocularity to season the discussion. That is reason, though not necessarily with understanding, lol. Logic has been a very useful tool in our attempts to be reasonable in delving into Reality, but it is very narrow in scope. It con only occasionally be used to any profit outside of mathematics and science. It is a formal form of thinking that has rules and process defined by certain steps and uses. Syllogisms, deduction, induction, etc, are forms of logic. I state this after the millionth time a Millennial has told me that something they mean to be 'understandable' they insist is also 'logical'. Millennials are an entire generation of people who need to be re-educated, or educated for the first time depending on how you define 'education'.