If-then Statements in Propositional Logic

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An if-then assertion or conditional assertion is a sort of compound assertion that’s linked by the phrases “if…then”. Logicians often used horseshoe () because the image for “if…then”. In some circumstances, logicians used the mathematical image “greater-than” (>) as a substitute of a horseshoe. 

Allow us to think about the instance beneath:

If the corporate closes down, then clearly many staff will endure. (p, q)

If we let p stand for the assertion “The corporate closes down” and q for the assertion “Clearly many staff will endure”, then the conditional assertion is symbolized as follows:

p q

If we use the greater-than image, then the assertion above is symbolized as follows:

p > q

You will need to observe that the assertion that precedes the connective horseshoe () is known as the “antecedent” and the proposition that comes after it’s referred to as “consequent.” Therefore, within the instance above, the antecedent is “The corporate closes down”, whereas the consequent is “Clearly many staff will endure”.

It is usually vital to notice that there are circumstances whereby the phrases “if…then” will not be talked about within the assertion, but it stays a conditional one. Allow us to think about the next instance:

Supplied that the catalyst is current, the response will happen. (p, q)

If we analyze the assertion, it is vitally clear that it’s conditional as a result of it suggests a “trigger and impact” relation. Thus, the assertion will be acknowledged as follows:

If the catalyst is current, then the response will happen. (p, q)

If we let p stand for the assertion “Supplied that the catalyst is current” and q for “The response will happen”, then the assertion is symbolized as follows:

p q

It’s equally vital to notice that typically the antecedent is acknowledged after the consequent. If this occurs, then now we have to represent the assertion accordingly. Allow us to take the instance beneath.

The portray have to be very costly if it was painted by Michelangelo. (p, q)

If we analyze the assertion, it’s clear that the antecedent is “It was painted by Michelangelo” and the ensuing is “The portray have to be very costly”.

Now, if we let p stand for “The portray have to be very costly” and q for “It was painted by Michelangelo”, then assertion “The portray have to be very costly if it was painted by Michelangelo” is symbolized as follows:

q p

Please observe that we symbolized the assertion “The portray have to be very costly if it was painted by Michelangelo” as q p as a result of in symbolizing if-then or conditional statements, we all the time write the antecedent first after which the ensuing. By the best way, please observe that the variables supplied after the assertion signify the statements in the complete assertion respectively. Thus, within the assertion

The portray have to be very costly if it was painted by Michelangelo. (p, q)

the variable p stands for the assertion “The portray have to be very costly” and q stands for the assertion “It was painted by Michelangelo”. Once more, since q is our antecedent and p is our consequent, and since in symbolizing if-then assertion we have to write the antecedent first after which the ensuing, so the assertion “The portray have to be very costly if it was painted by Michelangelo” is symbolized as follows:

q p

Guidelines in If-then Statements

  1. An If-then assertion is false if the antecedent is true and the ensuing false.
  2. Thus, aside from this type, the If-then assertion is true.

The reality desk beneath illustrates this level.

The reality desk above says:

  1. If p is true and q is true, then  q is true.
  2. If p is true and q is false, then  q is false.
  3. If p is false and q is true, then  q is true.
  4. If p is false and q is false, then  q is true.

As we will see, the principles in If-then statements or conditional statements say that the one occasion whereby the conditional assertion turns into false is when the antecedent is true and the ensuing false. Allow us to think about the instance beneath.

If it rains right this moment, then the street is moist.

Now, the primary row within the reality desk above says that p is true and is true. So, clearly,  q is true. It’s because, whether it is true that “it rains right this moment,” then it should even be true that “the street is moist.”

The second row says that p is true and q is false. So,  q have to be false. It’s because whether it is true that “it rains right this moment” then it should essentially comply with that “the street is moist.” Nonetheless, it’s stated that q is false, that’s, the street will not be moist; therefore, the conditional assertion is fake. Once more, it’s not possible for the street to not get moist if it rains.

The third row says p is false and q is true. If so, then  q is true. It’s because whether it is false that it rains right this moment (in different phrases, it doesn’t rain right this moment), it doesn’t essentially comply with that the street is dry. Even when it doesn’t rain, the street should be moist as a result of, for instance, a fireplace truck passes by and spills water on the street.Lastly, the fourth row within the reality desk above says p is false and q is false. If so, then  q is true. It’s because, primarily based on the instance above, it says “it doesn’t rain right this moment” and the “street will not be moist.” So, clearly, the conditional assertion is true.



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