**Understanding Logic**

Logic is a practical branch of philosophy based on reasoning, and at the same time as the basis of philosophy and as a means of science. With a function as the basis of philosophy and a means of science because logic is a “bridge” between philosophy and science, which is terminologically defined logic: The theory of valid inference. Basically, inference starts from a certain point of view, which then draws a conclusion. Legitimate inference, meaning that it is in accordance with logical and coherent considerations so that it can be traced back which is also true, which means that the correct form is required according to the content.

Logic as a theory of inference, is based on a concept that is expressed in the form of words or terms, and can be expressed in the form of a set so that each concept has a set, has a breadth. On the basis of a set because all the elements of reasoning in the logic of proof use a set diagram, and this is a formal proof if it is expressed by a valid and correct set diagram because the reasoning is valid and correct.

Based on the process of reasoning and also the nature of the conclusions it generates, logic is distinguished between deductive logic and inductive logic. Deductive logic is a system of reasoning that examines the principles of valid inference based on its form and the conclusions that are generated as necessities derived from the origin of the thought. In this logic, what is mainly examined is the form of the work of the mind if it is coherent and in accordance with logical considerations which can be proven that there are no other conclusions because the process of conclusions is correct and valid. Deductive logic because it talks about the relationship between the main forms of statements regardless of what content is described, because deductive logic is also called formal logic.

Inductive logic is a system of reasoning that examines the principles of valid inference from a number of specific points to a general, probable conclusion. This logic is often called material logic, which is trying to find the principles of reasoning that depend on their conformity with reality, therefore the conclusion is only probable, in the sense that as long as the conclusion is there there is no evidence to deny it, the conclusion is correct, and cannot be said to be certain. .

**Logic Language**

Language is a statement of thoughts or feelings as a means of human communication. And especially for scientific communication tools, it is called scientific language, namely news sentences which are statements or opinions. Language is also very important in the formation of scientific reasoning because scientific reasoning learns how to make proper descriptions and in accordance with proofs correctly and clearly. Language is generally distinguished between natural language and artificial language. Natural language is everyday language used to express something, which grows on the basis of the influence of the natural surroundings, distinguished between sign language and ordinary language. Artificial language is a language that is structured in such a way based on considerations of the mind for a specific purpose, distinguished between termi language and artificial language. This artificial language is what is meant by scientific language, an artificial language created by experts in their fields by using terms or symbols to represent certain meanings.

As a statement of thought or feeling and also as a means of human communication because language has 3 main functions, namely an expressive or emotive function, an affective or practical function, and a symbolic and logical function. Especially for logic and also for scientific language that must be considered is the symbolic function because scientific communication aims to convey information in the form of knowledge. In order for scientific communication to run well, the language used must be logically free from emotive elements.

The language expressed in the form of statements or declarative sentences can be divided into two types, namely analytic statements and synthetic statements.

Statements in logic in terms of the form of meaningful relationships they contain, these statements are likened to propositions. Propositions or statements based on the form of their content can be distinguished between 3 types, namely single propositions, categorical propositions, and compound propositions.

The three kinds of propositions or statements above which are the basis of reasoning are categorical propositions for categorical reasoning, and compound propositions for multiple reasoning. Single propositions or simple propositions can be processed into categorical reasoning and can also be included in multiple reasoning.

**The History of the Development of Logic** Logic was first conceived by Aristotle (384-322 BC), as a science of the laws of thought in order to maintain the line of thought from every mistake. Logic as a new science at that time was called “analytic” and “dialectic”. Aristotle’s collection of writings on logic is called Organon, which consists of six parts.

Theoprastus (371-287 BC), made the greatest contribution to logic is his interpretation of the possible meaning and also about the nature of each conclusion. Then, Porphyrius (233-306 AD), a scholar in Alexandria added a new section in the study of logic. This new section is called the Eisagoge, which is an introduction to the Categorie. This new section discusses the environments of matter and environmental properties in nature, which are commonly referred to as classification. Thus, logic becomes seven parts.

The figure of logic in the Islamic era was Al-Farabi (873-950 AD) who was known to be proficient in Old Grik, copying all of Aristotle’s writings in various fields of science and the writings of other Grik thinkers. Al-Farabi copied and commented on the seven parts of logic and added one new part so that it became eight parts.

Aristotle’s work on logic in the book Organon is known in full to the West after the extensive copying of many Islamic scholars into Latin. These extensive copies opened the West back to the mindset of the Old Grik.

Petrus Hispanus (died 1277 AD) compiled logic lessons in the form of poetry, such as All-Akhdari in the Islamic world, and his book became the basic book for logic lessons until the 17th century. Petrus Hispanus was the first to use various names for valid inference systems in relation to categorical syllogistic forms in a poem. And Peter Hispanus’s collection of poems on this logic is called Summulae.

Francis Bacon (1561-1626 AD) launched a disputed attack on logic and advocated the wider use of the induction system. Bacon’s attack on this logic received a warm welcome from various circles in the West, then more attention was paid to the use of the induction system.

The next logical reform in the West was followed by other authors including Gottfried Wilhem von Leibniz. He recommended replacing statements with symbols to make them more general in nature and easier to carry out analysis. Likewise, Leonard Euler, a Swiss mathematician and logician, conducted a discussion of terms using circles to describe the inter-term relationship which is known as circle-Euler.

John Stuart Mill in 1843 brought together the induction system with the deduction system. Every major thought in deduction requires induction and on the other hand induction requires deduction for the formation of thoughts about the results of experimentation and investigation. So, the two of them are not mutually exclusive parts, but actually help each other. Mill himself formulated methods for the induction system, known as the Four Methods.

Formal Logic After Mill’s time there were many new books and new commentaries on logic. And since the middle of the 19th century, a new branch called Symbolic-Logic was born. The pioneers of symbolic logic were basically started by Leibniz.

The first symbolic logic was developed by George Boole and Augustus de Morgan. Boole systematically used a wide range of symbols and methods of analysis according to mathematics, and Augustus De Morgan (1806-1871) was an English mathematician who made major contributions to symbolic logic with his thoughts on relations and negation.

Another character of symbolic logic, John Venn (1834-1923), tried to perfect Boole’s logical analysis by designing a circle diagram which is now known as the Venn diagram (Venn’s diagram) to describe relationships and check the validity of the inference of the syllogism. To describe the summarize or set aside relationships between subjects and predicates, each of which is considered a set.

The development of symbolic logic reached its peak in the early 20th century with the publication of 3 volumes of the writings of two great British philosophers Alfred North Whitehead and Bertrand Arthur William Russell entitled Principia Mathematica (1910-1913) with a total of 1992 pages. Russell-Whitehead’s paper Principia Mathematica provided a major impetus for the growth of symbolic logic.