What is a Pre-Existing Condition?

A necessary condition is a form of relationship in mathematics. If there is no A, there must be no B; if there is A and not necessarily B, then A is a necessary condition for B, which is written as B A, and read as B is contained in A. Mathematically, it is simply that if condition A can be derived from result B, we say that A is a necessary condition for B.

If there is no thing case A, there must be no thing case B, that is, if there is something case B, there must be thing case A, then A is a necessary condition for B. From a logical point of view, B can deduce A, and A is a necessary condition for B, which is equivalent to a sufficient condition for B to be A.

Suppose A is a condition and B is a conclusion

(1) B can be derived from A and A can be derived from B, then A is B's

Necessary conditions for life

Necessary conditions for investment

In life, "only ..., only ..." or "no ..., no ..." is often used to indicate necessary conditions. E.g:

1. A system and a government can only continuously improve their work and progress by constantly listening to their criticisms. (Premier Wen Jiabao's Talk on "Problem Milk Powder")

2. Only by working together can we get things done.

3. The correct pronunciation of this word can only be spoken before the Ark of the Covenant when the High Priest enters the Most Holy Place on the tenth day of July on the Jewish calendar.

4. No one offends me, I do not offend.

5. Failure to punish this murderous devil is not enough for civilian indignation.

6. There are no rules and no roundness.

When using "only ..., only ..." in life, people often do not consider adequacy. In other words, if A is not satisfied, B must not be established. We say that only A is B. This expresses the necessity of the condition. As to whether the condition A necessarily leads to B, we have not considered it. E.g:

Only one person who violates the criminal law can be punished in accordance with the provisions of the criminal law.

Objectively speaking, "violating the criminal law" is actually a necessary and sufficient condition that "penalties can be imposed in accordance with the provisions of criminal law." But in fact, when the speaker said this sentence, he just wanted to express that he could not impose a penalty in accordance with the provisions of the criminal law when he did not meet the violation of criminal law. As far as everyone knows that "violating the criminal law requires punishment in accordance with the provisions of the Criminal Law", it is not the meaning of the speaker.

So "only ..., only ..." in life just expresses the meaning that conditions are necessary and necessary, without considering sufficiency, which is different from the strict definition of logic.

Other terms of necessary conditions: necessary conditions, necessary conditions, necessary conditions.

Necessary condition for "only ..., only ..."

Necessary conditions for companies to winter

Although "only ..., only ..." expresses the necessity of a sentence pattern, many times the conditions it elicits are not only necessary but also sufficient, in fact, they are sufficient and necessary. E.g:

1. The wine can only be marked with the year of the year if it is produced from the grape juice extracted from the grapes of the current year.

2. The employer can terminate the labor contract only if the employee is proved to be ineligible during the probation period.

In these three examples, conditions are both necessary and sufficient. Therefore, it is still logical to change "only" to "as long as" in the sentence. But the semantics of the two expressions are different.

"Only" emphasizes the necessity and neglects the sufficiency, that is, it emphasizes that "when the grape juice extracted from the grapes of the current year is not used for production, wine cannot be marked with the current year", and "the grape juice extracted from the grapes of the current year is The raw materials are produced, and the wine can be marked with the year of the current year. "

If the sentence is changed to "As long as the grape juice extracted from the grapes of the current year is used as the raw material for production, the wine can be marked with the year of the year" is also logical.

"As long as" emphasizes sufficiency and neglects the necessity, that is, "the production of grape juice extracted from the grapes of the current year is used as the raw material, the wine can be marked with the year of the year", and "the grape juice not extracted from the grapes of the current year is The production of raw materials, wine can not be marked with the year of the current year. "

Such examples are not uncommon in life. E.g:

He only understood the matter after a brief explanation.

He only needed to explain the matter after a while.

What is the difference between these two sentences? Why sometimes emphasize the necessity and sometimes the sufficiency?

Actually it depends on the speaker's preset. Presupposition refers to a kind of pre-established information implied in the sentence, which usually manifests in the communication as a kind of background knowledge that both parties can understand and accept. For example: "He lost his pen" preset "He has a pen". The sentence "This matter can be understood only after explaining it for a while" The presupposition is more complicated and will not be clear at one and a half; the sentence "It only takes a while to explain and he will understand" The presupposition is simple, It can be explained plainly. Due to different presets, the speaker uses different related words.

The most common case is: "Only, only ..." presets "difficulty, only method"; "As long as ..., ..." preset "easy".

Example: You can be convinced only by interviewing him. --difficult

As long as you interview him, you can convince him. --easy

Prerequisite logic

Definition: If there is no thing case A, there must be no thing case B; if there is something case B, there must be thing case A, A is a necessary condition for B, it should be noted that the necessary condition is not an abbreviation of necessary and insufficient condition .

The necessary conditions are derived from logic when studying hypothetical propositions and hypothetical reasoning.

The hypothetical proposition that states that the condition of one thing is the condition of another is called the necessary condition hypothesis. The general form of the necessary condition hypothesis is: only p, only q. The symbol is: p q (read as "p inverse implication q"). For example, "only if there is a motive for committing a crime will it be a criminal" is a necessary condition hypothesis.

Reasoning based on the logical nature of the necessary condition hypothesis is called necessary condition hypothesis.

Necessary conditional hypothesis is a kind of reasoning that takes the necessary conditional hypothesis as the major premise and deduces it according to the logical nature of the precondition and the consequent relationship of the necessary conditional hypothesis. This reasoning is often used in investigative work and has been proven by long-term investigative practice. Therefore, it is of great significance to study and discuss its specific application in the investigation. The main task of criminal investigation is to arrest the perpetrators. The key step for apprehending the perpetrators is to find out what the perpetrators must have before committing an investigation. Because only in this way, can "according to the figure", focus on the examination of eligible people. "In specific investigative work, how can we find out what the perpetrators must have to commit the crime? The practical experience of many excellent investigators tells us that one of the better ways is to use the necessary postulates of the affirmative reasoning. The reasoning of this reasoning can be used to infer the conditions that the perpetrator should have, because there is a conditional connection between objective things: if one phenomenon or situation does not appear or does not exist, then another phenomenon or The situation must not appear or exist; while another phenomenon or situation appears or exists, a certain phenomenon or situation must appear or exist, that is, without P, there must be no q, and with q, there must be p; and the necessary condition hypothesis Propositions reflect exactly this kind of connection. Therefore, based on this kind of conditional connection, combined with the conditions grasped by site surveys and investigation visits, and using the affirmative postcondition of the necessary condition hypothetical reasoning, another phenomenon q will inevitably appear. Inferring the occurrence of a certain phenomenon P, inferring the conditions that the perpetrator should have committed the crime ^[1] .

Prerequisites Mathematics

There are propositions p and q. If p infers q, then p is a sufficient condition for q, and q is a necessary condition for p. If p infers q and q infers p, then p is a necessary and sufficient condition for q.

For example: x = y introduces x ^ 2 = y ^ 2, then x = y is a sufficient condition for x ^ 2 = y ^ 2, x ^ 2 = y ^ 2 is a necessary condition for x = y (x is a negative number, y When it is a positive number, x = y cannot be derived). (X ^ 2 represents the square of x)

a, b-positive-negative ab <0, ab <0, a, b-positive-negative, then a, b-positive-negative and ab <0 are mutually sufficient and necessary conditions.