九乡新闻网陈氏太极拳培训:"If and only if" vs. "if" or "only if", what'...
来源：百度文库 编辑：九乡新闻网 时间：2024/04/29 21:31:41
Formal logic including conditional or IF-Then statements appear in 3 out of 4 LSAT test sections. Both Logical Reasoning Sections and the Analytical Reasoning Section will use formal logic. This often includes conditional statements such as “IF Bob is selected THEN Suzie is also selected” or “Suzie is selected IF Bob is selected”
How does this statement differ from “Suzie is selected IF, AND ONLY IF Bob is selected”.
IF AND ONLY IF, is a biconditional statement, meaning that either both statements are true or both are false. So it is essentially and “IF” statement that works both ways.
So our statement “Suzie is selected IF, AND ONLY IF, Bob is selected” means that Suzie and Bob are either both selected or both not selected. There are a variety of standard logical symbols used to represent this relationship including:
“↔”, “⇔” and “≡”, and “iff”
For the purpose of diagramming your LSAT Logic Games we recommend the following:
Note that IF AND ONLY IF is different than simply ONLY IF.
Only If simply creates the reverse statement as if you used “IF”
So the statement “IF Mary is selected then Will is also selected” is the same as “Mary is selected ONLY IF Will is also selected” or “ONLY IF Will is select, is Mary selected”
All of which can be respresented as:
IF M –> W