What exactly does “either, or” mean?

When you’re mother asks if you would like cake or pie for dessert she probably means one or the other, but not both. Well the LSAT is not your mother, and in this rare instance the LSAT actually gives you more. You get to have either cake or pie OR BOTH!

Whenever you see “either A or B” on the LSAT it means you have have A or B or both A & B.

What about just OR?

Or works the same as either or. So A or B means A or B or both.

The exception!

Sometimes an LSAT question will specify that you have “either A or B, but not both.” Obviously in this case you cannot have both. This just gives you either A or B.

Learn more in our LSAT Prep Course.

The word UNLESS can be a blessing or a curse on the LSAT. This quick lesson will help make it a blessing for you.

Check out the bottom of this article for more LSAT articles, lessons and tips.

Unless is often found in the more difficult Logical Reasoning questions as well as in the Logic Games section of the LSAT.

Here are some of the LSAT questions where you’ll find UNLESS::

• Logical Reasoning
  • Necessary Assumptions
  • Sufficient Assumptions
  • Questions with Formal Logic or Conditional Reasoning Arguments
  • Many of the more difficult Logical Reasoning Questions
• Logic Games (Analytical Reasoning)
  • Many Grouping Games
  • Games with formal logic or conditional reasoning
  • Some of the more difficult logic games

UNLESS is often used on the LSAT to create complex logical structures that frequently confuse or slow down LSAT students.

If you know how to properly approach UNLESS statements you can make some of the more difficult LSAT questions much easier!

Here’s how to make UNLESS statements easy

Let’s start with a simple UNLESS statement:

You cannot fly unless you have wings

This statement is relatively simple so you don’t really need to change it in order to understand the meaning. But on the LSAT they can get much more complex than this, and if this statement were in a logic game you would still want to simplify to help with your game diagram and rules.

The process of simplifying an UNLESS statement is the same for any complex formal logic or conditional reasoning statement – you want to turn it into a basic IF – THEN statement. This makes it much easier to read and understand logically and will help you answer the question faster and more accurately. It also helps you diagram the statement quickly and easily for logic games.

IF – THEN statements are simply a statement with two parts – the first part follows the word IF and is the sufficient condition, the second part follows the word THEN and is the necessary condition. Don’t worry too much about the idea of “sufficient and necessary conditions right now” they’re not necessary in order to understand and utilize this concept.

In order to convert ANY UNLESS statement into a basic IF THEN statement you just need to follow the following steps:

1. Separate the statement into two parts (in this case Part 1: Cannot Fly, Part 2: have wings)
2. Pick one part. Either one, it doesn’t matter. (let’s pick Part 1: Cannot Fly)
3. Negate this part – this means to change if from positive to negative or in this case from negative (Cannot Fly) to positive (Can Fly)
4. Put that part first in your IF THEN statement – after the IF (so we get IF Can Fly)
5. Then take the other part and put it after the THEN – but don’t change or negate it at all (so we have THEN have wings)
6. You now have a complete IF THEN statement from your UNLESS statement (In this case: IF you can fly THEN you have wings)

The key elements here are to just pick any of the two parts, put it first (after the IF) and make sure you negate it. Also make sure you do not change the second part – the part that you put after THEN (don’t negate it)

Once you have this IF THEN statement you can also do the contra-positive of the statement for another IF THEN statement. For more on how to do this check out our complete LSAT courses.

Here’s another example from an actual LSAT question:

No form of psychotherapy that focuses on changing the patient’s unconscious beliefs and desires can be effective unless it also helps change beliefs that are under the patient’s direct conscious control.

Here’s our step by step approach

1. Two parts: Part 1: psychotherapy that focuses on changing the patient’s unconscious beliefs and desires CANNOT be effective Part 2: helps change beliefs that are under the patient’s direct conscious control
2. Pick one part. This time let’s try picking Part 2: helps change beliefs that are under the patient’s direct conscious control
3. Negate this part: It does NOT help change beliefs that are under the patient’s direct conscious control
4. Put that part first in your IF THEN statement – after the IF: IF it does NOT help change beliefs that are under patient control THEN …
5. Then take the other part and put it after the THEN – but don’t change or negate it at all: THEN psychotherapy that focuses on changing the patient’s unconscious beliefs and desires CANNOT be effective
6. You now have a complete IF THEN statement: IF it does NOT help change beliefs that are under patient control THEN psychotherapy that focuses on changing the patient’s unconscious beliefs and desires CANNOT be effective

Note that when we picked out Part 1: we changed it from “No form of psychotherapy… can be effective” to “psychotherapy….cannot be effective” – these two statements have the same meaning, but putting NO as CANNOT makes it a bit easier to understand. It can be very effective to simplify statements like this as you write them. For more on how to do this check out our complete LSAT courses.

So how will this help you on the exam? An IF THEN statement is much more useful as you know exactly what happens in a given situation. For example, now if you are told that a certain form of psychotherapy does NOT help change beliefs under patient control then you can answer easily that this psychotherapy that focuses on changing unconscious beliefs cannot be effective. For more on how to use this on actual LSAT questions and including lots of practice questions and explanations check out our complete LSAT courses.

Also, in the case of Logic Games you can use this to create a very simple rule for your diagrams.

You can also check out this complete question and explanation using unless statements. It’s a difficult question but it demonstrates how effective changing UNLESS to IF THEN can be on the LSAT.

Here’s some more LSAT articles to help you with formal logic and conditional reasoning:

• Necessary and Sufficient Conditions
• More Unless statements
• If and Only If
• Complete LSAT Courses

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You can find IF THEN statements with necessary and sufficient conditions in both the Logic Games and Logical Reasoning sections of the LSAT.
Here’s another look at our IF THEN statements…
IF A then B
A is our sufficient condition – if we have A then we will always have B or in other words A is sufficient to know that we must have B
B is our necessary condition – B is necessary or required in order to have A. So if we do not have B then we will not have A. We see this in our contra-positive IF not B then not A.

Here is a basic logical reasoning style examples of these conditions:
The local theatre will only produce a new play if it has seen previous success in another theatre. My play has never been successful in another theatre, therefore my play will not be produced by the local theatre.
The necessary condition here is that a play “has seen previous success in another theatre”
In the absence of this condition we do not achieve our other condition – the sufficient one.
The sufficient condition is “the local theatre producing a play”

If I tell you that Bob’s play was produced by the local theatre, then you know for sure that Bob’s play has seen previous success in other theatres as that is a requirement for this local theatre to produce it. So being produced locally is sufficient to know that the play saw success in another theatre.
Another way to look at necessary and sufficient conditions is this:

I require air to live. (air is a necessary condition for my life)
If I am alive tomorrow then you know I have air. (being alive is sufficient for you to know that I have air)

Here’s another example of a logical reasoning style question that uses necessary and sufficient conditions/formal logic to get to the correct answer.
Whenever you encounter a logical reasoning question that uses the following words, it can be a good idea to diagram some of the statements in the argument out. You only need to do this if you are having trouble understanding the logic of the argument, often it is easy to understand and faster without a diagram. But if you’re struggling, a quick diagram can help a lot.
The words that make for easier diagrams are:
IF THEN
ONLY IF
UNLESS
IF BUT ONLY IF
IF AND ONLY IF
The example with Miley Cyrus and LSAT conditional statements above is a great example of when diagramming helps.

Also here’s some more articles on formal logic & conditional reasoning.

For complete coverage of this topic and tonnes of practice questions explained. Check out our LSAT Prep Course.

Since Miley Cyrus would never date a boy who did not believe in marriage, and anyone who truly understands romance believes in marriage, only a boy who truly understands romance would have any chance of dating Miley Cyrus.

The reasoning in the argument is flawed because the argument ignores the possibility that some people who

(A) have no chance of dating Miley Cyrus do not truly understand romance
(B) truly understand romance have no chance of dating Miley Cyrus
(C) truly understand romance do not believe in marriage
(D) believe in marriage have no chance of dating Miley Cyrus
(E) believe in marriage do not truly understand romance

Read on for the explanation and answer…
This is a great example of a flaw LSAT question with formal logic or conditional reasoning. You’re looking to identify what’s wrong with the argument but first you’ll need to breakdown the conditional reasoning. Let’s start by drawing out our basic if-then statements:

We start with a couple of premises:

“Since Miley Cyrus would never date a boy who did not believe in marriage…”
and
“anyone who truly understands romance believes in marriage”

With any LSAT question involving conditional reasoning you want to turn the statements into basic IF-THEN statements. Our premises then become:

IF a boy does not believe in marriage THEN he cannot date Miley Cyrus
and
IF you understand romance THEN you believe in marriage

You can represent these graphically as follows:

Usually you would use just the letters B and D or BM and DM to represent belief in marriage and dating Miley Cyrus but we’ve used the full words here for ease of explanation. When you do this yourself on the actual or practice LSAT exams you should use only a single letter, it will speed things up.

These two IF-THEN statements are our premises and are known to be true for sure. We then have our conclusion which is suspect as it makes a conclusion that cannot be drawn on the basis of the two premises provided.

Our conclusion is a bit tricky as it’s an “ONLY IF” statement. The easy trick for these statements is to remember that you reverse the order of the statement when you turn it into a basic IF-THEN statement. e.g. ONLY IF A THEN B becomes
IF B THEN A or IF B –> A

Our conclusion was “only a boy who truly understands romance would have any chance of dating Miley Cyrus” or in IF-THEN terms:

ONLY IF understand romance THEN date Miley Cyrus
and reversing that to a basic IF-THEN statement we get:

IF Dating Miley Cyrus THEN understand romance

We can represent this graphically as:

So now we have our premises and conclusion expressed as IF-THEN statements. You can answer the question from here or you can go on to add some additional information by taking the contra-positives of each IF-THEN statement. For a detailed explanation of how to set up the contra-positive and IF-THEN statements check out this article, or try our LSAT Prep Course Online.

So here’s our complete story including contra-positives:

Premise 1:


Premise 2:

Conclusion:

So what’s wrong with our conclusion?  Our conclusion starts with the information on the left side of the IF THEN statement. Which is either “If you are dating Miley Cyrus” or from the contra-positive “If you don’t understand romance”

Let’s start with the first one: “If you are dating Miley Cyrus” – what do we know about someone who is dating Miley Cyrus? The way to find out is to skim read down the left side of all your equations in the premises. The premises are our facts so what we have there is known to be true. We skim the left side for something about a person “dating Miley” and we can then follow it to the right to find out more information. So we find the statement:

So we can conclude that if you’re dating Miley Cyrus, you believe in marriage. But our conclusion takes this further and concludes that you also understand romance. Can we go this far?  You can find out by continuing to follow the chain of logic in your premises, we’ve gone from dating Miley, to believing in marriage – what next? Nothing comes next! We have no statement that starts with belief in marriage on the left side and so we can draw no conclusions on this basis. So our conclusion went to far. It should have stopped with “Anyone who dates Miley Cyrus must believe in marriage.”  and not gone on to conclude they also understand marriage. So the error here is that the argument assumes that if you believe in marriage you also understand romance, or in other words and in the words of our question stem, it ignores the possibility that some people who believe in marriage do not truly understand romance.

With the information in our premises it’s possible that we have someone who dates Miley, believes in marriage but does not truly understand romance. This possibility was overlooked or ignored and so (E) is our correct answer.

If the novel were successful, it would be produced as a movie or adapted as a theatre script. However, this novel is not successful, therefore, we must conclude that it will neither become a movie nor will it be adapted as a theatre script.

The argument’s reasoning is flawed because the argument:

(A) fails to draw the conclusion that the novel will not both be produced as a movie and be adapted as a theatre script, rather than that it will do neither
(B) fails to explain in exactly what way the novel is unsuccessful
(C) equates the novel’s aesthetic worth with its commercial success
(D) presumes, without providing justification, that there are no further avenues for the novel other than production as a movie or adaptation as a theatre script
(E) fails to recognize that the novel’s not satisfying one sufficient condition does not preclude its satisfying a different sufficient condition for production as a movie or adaptation as a theatre script

This is a formal logic question. It uses conditional reasoning or if then statements.
For a full analysis of IF THEN statements and formal logic for logical reasoning questions see our free LSAT course: Formal Logic Tutorial
And here Practice Questions

Let’s analyze our stimulus.
Our first premise is: IF the novel is successful THEN movie or script
Our second premise: This novel is NOT successful.
Conclusion: NOT movie nor script

This is flawed formal logic. The mistake here is that we have reversed our IF THEN statement. As you can see from the tutorials in formal logic Formal Logic Tutorial you cannot reverse your IF THEN statement except as a contra positive. The contra positive of our IF THEN statement is as follows:

Original Statement: IF the novel is successful THEN movie or script
Contra-Positive: IF there is NOT a movie or script THEN the novel was NOT successful

There is nothing else you can conclude from this original statement or premise. This means that our conclusion is a flawed conclusion. The conclusion tries to state the following:

Conclusion: IF NOT successful THEN NOT movie or script.

We cannot draw this conclusion from our original premise. By drawing this conclusion we fail to recognize that the novel could become a movie or script by some other means than success. For example, maybe all novels about children are made into movies giving us the statement IF novel is about children THEN movie. This would give us another avenue to arrive at a movie or script despite the novel not being successful.

So our correct answer choice is (E). The argument fails to recognize that the novel’s not satisfying one sufficient condition (being successful) does not preclude its satisfying a different sufficient condition (some other means such as being about children) for production as a movie or adaptation as a theatre script.

The easiest way to look at this statement is as

IF not X then Y
OR
IF not Y then X

You can pick either one of the terms (X or Y) place them first and negate that term or make it the opposite and place the other term second. (to negate or make opposite just means to change “X” to “not X” or to change “not X” to “X”)

So “Not A unless B” becomes

If A then B
OR
If not B then not A

The term you put first in the IF-THEN statement is turned to the opposite meaning “Not A” becomes “A” or “A” becomes “Not A”

You can also look at Unless as essentially the same as saying “IF NOT”

So X Unless Y is the same as “X IF Not Y” or “IF Not Y then X”

Let’s try this in a sentence.

I will go to the park unless I stay home.

This is the same as “I will go to the park if I do not stay home” or…

IF Not Home then Park
IF Not Park then Home

Here’s some more practice statements translated into IF-THEN statements.

A unless B

If not A then B
If not B then A

Unless you apply the brakes, you will crash.

If Not Crash then Braked
If Not Braked then Crashed

You will fail this exam unless you study for it.

If Not Study then Fail
If Not Fail then Study

Note that as with your simple IF-THEN statements you cannot determine any additional information from theses statements. For example:

A unless B

Gives you:

If Not B then A
If Not A then B

But does not tell you anything if you are given A or B.

If A then ???
If B then ???

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