How to do the logical reasoning of civil servants' line test

Logical judgment is one of the difficulties in the national civil service examination. Although the number of questions is not large, it often takes up a lot of candidates' time. In fact, there are some skills to solve logical judgment problems. Mastering these skills can not only save time, but also help to solve problems correctly.

This paper introduces some common solutions to logical judgment questions, and gives an in-depth explanation with examples, hoping to give some inspiration and help to candidates.

I. Overview

The topics of logical judgment in the national civil service examination are divided into two types: inevitability reasoning and possibility reasoning. Inevitability reasoning has few topics, strong methodology and many theories involved. The number of possible reasoning topics is large and difficult, and the national civil service examination has gradually increased in recent years.

Necessary reasoning, also called deductive reasoning, refers to reasoning that can inevitably lead to true conclusions from true premises. If the premise is true, the conclusion must be true. Including: all kinds of outspoken reasoning, syllogism, conjoined reasoning, hypothetical reasoning, selective reasoning and modal reasoning. Possibility reasoning, also known as probability reasoning, is opposite to inevitability reasoning. It refers to the reasoning that the premise and conclusion have no implication relationship, which is mainly divided into inductive reasoning and analogical reasoning.

Common problem-solving methods of logical reasoning include venn diagram method, chart method, sorting method, substitution method, calculation method, hypothesis method, exclusion method, contradiction method, legislation, abstraction method, seeking common ground method, seeking difference method, * * variation method, residual method, finding causality and finding logical loopholes. Below we will choose the most important and practical method to explain to the candidates.

Second, the substitution method

Replacement method is one of the most commonly used methods. Usually, when the topic information is complicated or there is no idea about the answer to the topic, the substitution method can be used. Substitution method can be used for both inevitable reasoning (a conclusion must be derived from premise) and possible reasoning (there is no inevitable reasoning relationship between premise and conclusion).

1, inevitability reasoning

In inevitability reasoning, when the topic involves the commonly used substitution method of inferring conclusions from multiple conditions, the forward substitution method is generally adopted, that is, the option is substituted into the stem of the topic, and if it contradicts the stem of the topic, it is false.

Example 1: Someone asked the ages of A, B and C. A said, "I am 22 years old, 2 years younger than B and 0/year older than C." B said, "I am not the youngest. C is three years behind me and C is 25 years old. " C said, "I am younger than A, A is 23 years old, and B is 3 years older than A."

One of the above three sentences is deliberately wrong. Do you know the ages of these three people? ( )

A. A is 22 years old, B is 25 years old, and C is 2 1 year old.

B. A is 23 years old, B is 22 years old and C is 25 years old.

C. A is 22 years old, B is 23 years old, and C is 2 1 year old.

D a is 23 years old, b is 25 years old and c is 22 years old.

Problem solving analysis: It is more convenient to solve this problem with method of substitution. If item A is substituted, there is only one error in item A and two errors in item B, which does not meet the meaning of the question, so item A is wrong; When item B is substituted, there are two mistakes in A, which do not conform to the meaning of the question, so item B is wrong; If item C is substituted, there is only one mistake in A and two mistakes in B, which are inconsistent with the meaning of the question, so item C is wrong; If item D is substituted, Party A, Party B and Party C each have a mistake, which is in line with the meaning of the question.

So, the correct answer is D.

2. Possibility reasoning

In possibility reasoning, when solving preset problems, sometimes there are cases where multiple options can support the conclusion of the stem of the question or four options do not seem to be prerequisites. At this time, candidates can solve the problem by reverse substitution. That is, substitute the negation of the option into the stem. If the conclusion of the stem cannot be deduced, the option is the premise of the stem argument; On the other hand, if it does not affect the conclusion of the stem, then this option is not the premise of the stem argument.

Example 2: The Spring Festival Music Awards Ceremony broke the previous selection method of only one best golden song, and selected the best golden songs according to several music styles such as rock and jazz. In this way, the work of musicians can be treated more fairly, and listeners and music lovers can have more say in the quality of music.

According to the above information, the assumption implied by the change of this selection method is ().

A. Dividing musical styles can promote the music industry to let a hundred flowers blossom and a hundred schools of thought contend.

B. every song can be classified according to this, and there is no omission.

C. Both listeners and music lovers have their own favorite song styles.

D. The change of selection methods provides musicians with more opportunities to show themselves and realize their self-worth.

Problem solving analysis: The argument of the topic is that choosing the best golden songs according to the styles of rock and jazz can make musicians get a fairer treatment. The four options all support the question stem to some extent. In order to find an essential hypothesis for the argument of the stem, we can substitute the anti-proposition of the option into it. If you can't draw a conclusion in the stem, this option is a necessary implicit assumption. The counter-proposition of item B is "not every song can be classified in this way", which leads to some songs not appearing in the classified category, so they can't participate in the selection of the best songs, thus being treated unfairly. Therefore, item B is a necessary assumption to draw a conclusion, and the reverse substitution of options A, C and D will not affect the introduction of the conclusion, so these three options are unnecessary. So, the correct answer is B.

Third, the exclusion method.

Exclusion is very common in almost all multiple-choice questions, and it is no exception in logical judgment questions, but the application of exclusion in logical judgment questions is different from other questions.

1, inevitability reasoning

In inevitability reasoning, if there are multiple conditions in the topic, you can exclude the unqualified options first; Exclusion method can also be used in combination with other methods, for example, in the process of direct derivation or in the process of derivation by other methods, the wrong options can be excluded at the same time of derivation. For some questions, you can exclude all the wrong options first, and then export the correct options. Using this method can not only save time, but also ensure the correct rate.

At a party, Maggie met Tom, Carl and George. He wants to know what they do, but they only provide the following information: one is a lawyer, one is a salesman and the other is a doctor; George is older than the doctor, Tom is different from the salesman, and the salesman Bical is young.

Based on the above information, Maggie can draw the conclusion of ().

A. Tom is a lawyer, Carl is a salesman and George is a doctor.

Tom is a salesman, Carl is a doctor and George is a lawyer.

Tom is a doctor, Carl is a lawyer and George is a salesman.

Tom is a doctor, Carl is a salesman and George is a lawyer.

Problem solving analysis: It is not easy to judge the occupations of three people in the topic directly according to the known conditions. At this time, it is easier to solve the problem by exclusion. According to the two conditions of "Tom and salesman are different in age and salesman Bical is young", neither Tom nor Carl is a salesman, so only George is a salesman. According to this, options A, B and D can be excluded, and then we can easily get the answer is C. Therefore, the correct answer is C.

2. Possibility reasoning

In possibility reasoning, when looking for strengthening, weakening, explanation and preconditions, you can first exclude options that are irrelevant to the topic; When looking for the conclusion of the topic stem argument, in addition to excluding irrelevant items, you can also exclude options that contradict the topic stem argument. In addition, when some options are too absolute, they are often not the conclusion of the argument and can be ruled out.

Example 2: "Gene food" such as nucleic acid in the name of health care products is not helpful to human health. From a scientific point of view, it is not true that the human body needs to supplement foreign nucleic acids. What the human body lacks is nutrition, and nucleic acid cannot be lacking. Some advertisements say that people's ability to make genes will be weakened when they are old and sick, which is even more nonsense.

From this, () can be deduced.

A. people get sick because of malnutrition.

B. The nucleic acid in human body will decrease with age.

C. all advertisements about health care products lack scientific basis.

D. Eating health products may not necessarily improve health.

Problem-solving analysis: This is a conclusive problem, and the direct use of exclusion method can reduce the problem-solving time. Because there is no mention of the relationship between disease and nutrition in the title, item A is irrelevant and excluded; It is clearly pointed out in the stem that nucleic acid cannot be lacking, so item B is the wrong option and is excluded; The expression of item C is too absolute, and it is obviously incorrect to expand the topic discussion to all health care products, so it is excluded. Therefore, item D can only be deduced from the stem. So, the correct answer is D.

Four. Law of contradiction

When a topic has many sentences that tell us how true and false it is, we can try to find the contradictory relationship and solve the problem in contradictory ways. Two contradictory propositions must have one truth and one falsehood. Common contradictions are as follows:

Explicit proposition: "all s are p" and "some s are not p";

"not all s are p" and "some s are p";

"An S is P" and "An S is not P"

Complex propositions: "P and Q" and "Non-P or Non-Q";

"or p, or q" and "not p, not q";

"If P, then Q" and "P is not Q";

"only p, only q" and "no p, no q"

Example: Shakespeare wrote in The Merchant of Venice that Portia, a girl from a rich family, had both good looks and good looks, and her nobles, sons and grandchildren proposed to her one after another. According to his father's will, Portia was engaged by the suitor. Portia has three boxes of gold, silver and lead, each engraved with three sentences. Only one box contains a portrait of Portia. Guess which box Portia's portrait is put in first through these three sentences. The suitor can marry Portia. The gold box says, "The portrait is not in this box." The silver box says, "The portrait is in the lead box." The lead box says, "The portrait is not in this box."

Portia told the suitor that only one of the above three sentences was true. In which box is the portrait of Portia? ( )

A. golden box

B. silver box

C. lead box

D. uncertainty

Problem-solving analysis: It is pointed out in the title that at most one of the three sentences is correct, so contradictions can be used to solve problems. Let's find out two contradictory boxes first, so besides these two boxes, the third one is the box that tells lies. In the title, the silver plate said that "the portrait is in the lead box", and the lead box said that the portrait is not in the lead box, which constitutes a contradictory relationship, and there must be one truth and one falsehood. It can be confirmed that the rest of the gold box is fake, that is, "the portrait is in the gold box."

So, the correct answer is A.

V. Violating the law

When there are many sentences in a topic that tell us that there is only one truth or one falsehood, and no contradiction can be found, we can try to find the opposite relationship or the opposite relationship and solve the problem by the opposite method. The two opposing propositions must be false, and the common oppositions are as follows:

"all s are p" and "all s are not p";

"all s are p" and "one s is not p";

"all s are not p" and "one s is p"

There must be a truth between two opposing propositions, and the common opposition is as follows:

"some s are p" and "some s are not p";

"some s are not p" and "some s are p";

"some s are p" and "some s are not p"

In the civil service examination, opposition is more common than opposition.

A company has 20 employees, including the general manager. Regarding these 20 employees, only one of the following three conclusions is correct:

Someone invested in this company.

Two. Someone didn't share in the company.

Three. The general manager didn't share the shares in the company.

According to the above facts, which of the following is correct? ( )

A.all A.20 employees have joined the stock market.

None of the employees of B.B.20 have taken a stake.

C. Only one person joined the stock market.

D. only one person didn't get a piece of the action.

Problem-solving analysis: when we can't find the contradictory relationship, if we can find the proposition with antagonistic relationship or lower, it can also help us solve the problem quickly. In the title, the affirmative proposition "someone has invested in the company" and the negative proposition "someone has not invested in the company" constitute a pair of opposites. These two propositions cannot be false, but there must be a truth. Because only one of the three conclusions is true, "the general manager didn't invest in the company" is a false proposition, from which it can be concluded that "the general manager invested in the company" and then it can be concluded that "someone invested in the company" is true, then the proposition that "someone didn't invest in the company" is false, so it can be concluded that "all 20 employees invested in the company", that is, item A is correct. So, the correct answer is A.