{"id":612,"date":"2025-05-14T18:56:13","date_gmt":"2025-05-14T18:56:13","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/?post_type=chapter&p=612"},"modified":"2025-07-13T21:45:45","modified_gmt":"2025-07-13T21:45:45","slug":"deductive-reasoning","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/chapter\/deductive-reasoning\/","title":{"raw":"Deductive Reasoning","rendered":"Deductive Reasoning"},"content":{"raw":"The second type of reasoning is called deductive reasoning<\/strong>, or deduction, a type of reasoning in which a conclusion is based on the combination of multiple premises that are generally assumed to be true. It has been referred to as \u201creasoning from principle,\u201d which is a good description. It can also be called \u201ctop-down\u201d reasoning. However, you should not think of deductive reasoning as the opposite of inductive reasoning. They are two different ways of thinking about evidence.\r\n
\r\n\r\nDeductive reasoning<\/strong>\r\n\r\na type of reasoning in which a conclusion is based on the combination of multiple premises that are generally assumed to be true\r\n\r\n<\/div>\r\n
\r\n\r\nFirst, formal deductive reasoning employs the syllogism<\/strong>, which is a three-sentence argument composed of a major premise (a generalization or principle that is accepted as true), a minor premise (an example of the major premise), and a conclusion. This conclusion has to be true if the major and minor premise are true; it logically follows from the first two statements. Here are some examples. The most common one you may have seen before.<\/span>\r\n
\r\n\r\nAll men are mortal. (Major premise: something everyone already agrees on)<\/em>\r\n\r\nSocrates is a man. (Minor premise: an example taken from the major premise.)<\/em>\r\n\r\nSocrates is mortal. (Conclusion: the only conclusion that can be drawn from the first two sentences.)<\/em>\r\n\r\n<\/div>\r\n
\r\n\r\n\u00a0<\/em>\r\n\r\nMajor Premise: All State College students must take COMM 1110. <\/em>\r\n\r\nMinor Premise: Brittany is a State College student.<\/em>\r\n\r\nConclusion: Brittany must take COMM 1110.<\/em>\r\n\r\n<\/div>\r\n
\r\n\r\nMajor Premise: All dogs have fur. <\/em>\r\n\r\nMinor Premise: Fifi is a dog.<\/em>\r\n\r\nConclusion: Fifi has fur.<\/em>\r\n\r\n<\/div>\r\nOf course, at this point, you may have some issues with these examples. First, Socrates is already dead and you did not need a syllogism to know that. The Greek philosopher lived 2,400 years ago! Second, these seem kind of obvious. Third, are there some exceptions to \u201cAll Dalton State College students must take COMM 1110\u201d? Yes, there are; some transfer students do not, and certificate students do not. Finally, there are breeds of dogs that are hairless. Some people consider them odd-looking, but they do exist. So while it is true that all men are mortal, it is not absolutely and universally true that all State College students must complete COMM 1110 or that all dogs have fur.\r\n
\r\n\r\nSyllogism<\/strong>\r\n\r\na three-sentence argument composed of a major premise (a generalization or principle that is accepted as true), a minor premise (and example of the major premise), and a conclusion\r\n\r\n<\/div>\r\nConsequently, the first criterion for syllogisms and deductive reasoning is that the premises have to be true for the conclusion to be true, even if the method is right. A right method and untrue premises will not result in a true conclusion. Equally, true premises with a wrong method will also not result in true conclusions. For example:\r\n
\r\n\r\nMajor premise: All dogs bark. <\/em>\r\n\r\nMinor premise: Fifi barks.<\/em>\r\n\r\nConclusion: Fifi is a dog.<\/em>\r\n\r\n<\/div>\r\n
\r\n\r\nYou should notice that the minor premise is stated incorrectly. We know other animals bark, notably seals (although it is hard to think of a seal named \u201cFifi\u201d). The minor premise would have to read \u201cFifi is a dog\u201d to arrive at the logical conclusion, \u201cFifi barks.\u201d (Also, there are dog breeds that do not bark.) However, by restating the major premise, you have a different argument.<\/span>\r\n
\r\n\r\nMajor premise: Dogs are the only animals that wag their tails when happy.<\/em>\r\n\r\nMinor premise: Fifi wags her tail when happy. <\/em>\r\n\r\nConclusion: Fifi is a dog.<\/em>\r\n\r\n<\/div>\r\nAnother term in deductive reasoning is an enthymeme<\/strong>. This odd word refers to a syllogism with one of the premises missing.\r\n
\r\n\r\nMajor premise: (missing)<\/em>\r\n\r\nMinor premise: Daniel Becker is a chemistry major. <\/em>\r\n\r\nConclusion: Daniel Becker will make a good SGA president.<\/em>\r\n\r\n<\/div>\r\nWhat is the missing major premise? \u201cChemistry majors make good SGA presidents.\u201d Why? Is there any support for this statement? Deductive reasoning is not designed to present unsupported major premises; its purpose is to go from what is known to what is not known in the absence of direct observation. If it is true that chemistry majors make good SGA presidents, then we could conclude Dan will do a good job in this role. But the premise, which in the enthymeme is left out, is questionable when put up to scrutiny.\r\n
\r\n\r\nMajor premise: Socialists favor government-run health care. <\/em>\r\n\r\nMinor premise: (missing)<\/em>\r\n\r\nConclusion: Candidate Fran Stokes favors government-run health care.<\/em>\r\n\r\n<\/div>\r\nThe missing statement in the minor premise, \u201cFran Stokes is a socialist,\u201d is left out so that the audience can make the connection, even if it is erroneous. Consequently, it is best to avoid enthymemes with audiences and to be mindful of them when used by persuaders. They are mentioned here to make you aware of how commonly they are used as shortcuts. Enthymemes are common in advertising. You may have heard the slogan for Smucker\u2019s jams, \u201cWith a name like Smucker\u2019s, it has to be good.\u201d\r\n
\r\n\r\nMajor premise: Products with odd names are good products. (questionable!)<\/em>\r\n\r\nMinor premise: \u201cSmucker\u2019s\u201d is an odd name. <\/em>\r\n\r\nConclusion: Smucker\u2019s is a good product.<\/em>\r\n\r\n<\/div>\r\n
\r\n\r\nEnthymeme<\/strong>\r\n\r\na syllogism with one of the premises missing\r\n\r\n<\/div>\r\nTo conclude, deductive reasoning helps us go from known to unknown and can lead to reliable conclusions if the premises and the method are correct. It has been around since the time of the ancient Greeks. It is not the flipside of inductive but a separate method of logic. While enthymemes are not always errors, you should listen carefully to arguments that use them to be sure that something incorrect is not being assumed or presented.\r\n\r\n<\/div>\r\n<\/div>","rendered":"

The second type of reasoning is called deductive reasoning<\/strong>, or deduction, a type of reasoning in which a conclusion is based on the combination of multiple premises that are generally assumed to be true. It has been referred to as \u201creasoning from principle,\u201d which is a good description. It can also be called \u201ctop-down\u201d reasoning. However, you should not think of deductive reasoning as the opposite of inductive reasoning. They are two different ways of thinking about evidence.<\/p>\n

\n

Deductive reasoning<\/strong><\/p>\n

a type of reasoning in which a conclusion is based on the combination of multiple premises that are generally assumed to be true<\/p>\n<\/div>\n

\n

First, formal deductive reasoning employs the syllogism<\/strong>, which is a three-sentence argument composed of a major premise (a generalization or principle that is accepted as true), a minor premise (an example of the major premise), and a conclusion. This conclusion has to be true if the major and minor premise are true; it logically follows from the first two statements. Here are some examples. The most common one you may have seen before.<\/span><\/p>\n

\n

All men are mortal. (Major premise: something everyone already agrees on)<\/em><\/p>\n

Socrates is a man. (Minor premise: an example taken from the major premise.)<\/em><\/p>\n

Socrates is mortal. (Conclusion: the only conclusion that can be drawn from the first two sentences.)<\/em><\/p>\n<\/div>\n

\n

\u00a0<\/em><\/p>\n

Major Premise: All State College students must take COMM 1110. <\/em><\/p>\n

Minor Premise: Brittany is a State College student.<\/em><\/p>\n

Conclusion: Brittany must take COMM 1110.<\/em><\/p>\n<\/div>\n

\n

Major Premise: All dogs have fur. <\/em><\/p>\n

Minor Premise: Fifi is a dog.<\/em><\/p>\n

Conclusion: Fifi has fur.<\/em><\/p>\n<\/div>\n

Of course, at this point, you may have some issues with these examples. First, Socrates is already dead and you did not need a syllogism to know that. The Greek philosopher lived 2,400 years ago! Second, these seem kind of obvious. Third, are there some exceptions to \u201cAll Dalton State College students must take COMM 1110\u201d? Yes, there are; some transfer students do not, and certificate students do not. Finally, there are breeds of dogs that are hairless. Some people consider them odd-looking, but they do exist. So while it is true that all men are mortal, it is not absolutely and universally true that all State College students must complete COMM 1110 or that all dogs have fur.<\/p>\n

\n

Syllogism<\/strong><\/p>\n

a three-sentence argument composed of a major premise (a generalization or principle that is accepted as true), a minor premise (and example of the major premise), and a conclusion<\/p>\n<\/div>\n

Consequently, the first criterion for syllogisms and deductive reasoning is that the premises have to be true for the conclusion to be true, even if the method is right. A right method and untrue premises will not result in a true conclusion. Equally, true premises with a wrong method will also not result in true conclusions. For example:<\/p>\n

\n

Major premise: All dogs bark. <\/em><\/p>\n

Minor premise: Fifi barks.<\/em><\/p>\n

Conclusion: Fifi is a dog.<\/em><\/p>\n<\/div>\n

\n

You should notice that the minor premise is stated incorrectly. We know other animals bark, notably seals (although it is hard to think of a seal named \u201cFifi\u201d). The minor premise would have to read \u201cFifi is a dog\u201d to arrive at the logical conclusion, \u201cFifi barks.\u201d (Also, there are dog breeds that do not bark.) However, by restating the major premise, you have a different argument.<\/span><\/p>\n

\n

Major premise: Dogs are the only animals that wag their tails when happy.<\/em><\/p>\n

Minor premise: Fifi wags her tail when happy. <\/em><\/p>\n

Conclusion: Fifi is a dog.<\/em><\/p>\n<\/div>\n

Another term in deductive reasoning is an enthymeme<\/strong>. This odd word refers to a syllogism with one of the premises missing.<\/p>\n

\n

Major premise: (missing)<\/em><\/p>\n

Minor premise: Daniel Becker is a chemistry major. <\/em><\/p>\n

Conclusion: Daniel Becker will make a good SGA president.<\/em><\/p>\n<\/div>\n

What is the missing major premise? \u201cChemistry majors make good SGA presidents.\u201d Why? Is there any support for this statement? Deductive reasoning is not designed to present unsupported major premises; its purpose is to go from what is known to what is not known in the absence of direct observation. If it is true that chemistry majors make good SGA presidents, then we could conclude Dan will do a good job in this role. But the premise, which in the enthymeme is left out, is questionable when put up to scrutiny.<\/p>\n

\n

Major premise: Socialists favor government-run health care. <\/em><\/p>\n

Minor premise: (missing)<\/em><\/p>\n

Conclusion: Candidate Fran Stokes favors government-run health care.<\/em><\/p>\n<\/div>\n

The missing statement in the minor premise, \u201cFran Stokes is a socialist,\u201d is left out so that the audience can make the connection, even if it is erroneous. Consequently, it is best to avoid enthymemes with audiences and to be mindful of them when used by persuaders. They are mentioned here to make you aware of how commonly they are used as shortcuts. Enthymemes are common in advertising. You may have heard the slogan for Smucker\u2019s jams, \u201cWith a name like Smucker\u2019s, it has to be good.\u201d<\/p>\n

\n

Major premise: Products with odd names are good products. (questionable!)<\/em><\/p>\n

Minor premise: \u201cSmucker\u2019s\u201d is an odd name. <\/em><\/p>\n

Conclusion: Smucker\u2019s is a good product.<\/em><\/p>\n<\/div>\n

\n

Enthymeme<\/strong><\/p>\n

a syllogism with one of the premises missing<\/p>\n<\/div>\n

To conclude, deductive reasoning helps us go from known to unknown and can lead to reliable conclusions if the premises and the method are correct. It has been around since the time of the ancient Greeks. It is not the flipside of inductive but a separate method of logic. While enthymemes are not always errors, you should listen carefully to arguments that use them to be sure that something incorrect is not being assumed or presented.<\/p>\n<\/div>\n<\/div>\n","protected":false},"author":133,"menu_order":3,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-612","chapter","type-chapter","status-publish","hentry"],"part":603,"_links":{"self":[{"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/pressbooks\/v2\/chapters\/612","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/wp\/v2\/users\/133"}],"version-history":[{"count":2,"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/pressbooks\/v2\/chapters\/612\/revisions"}],"predecessor-version":[{"id":855,"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/pressbooks\/v2\/chapters\/612\/revisions\/855"}],"part":[{"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/pressbooks\/v2\/parts\/603"}],"metadata":[{"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/pressbooks\/v2\/chapters\/612\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/wp\/v2\/media?parent=612"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/pressbooks\/v2\/chapter-type?post=612"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/wp\/v2\/contributor?post=612"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/ppsccom1150publicspeaking\/wp-json\/wp\/v2\/license?post=612"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}