Lesson 1.3 — NOT

The Word

NOT flips a sentence. It takes whatever the sentence says and gives you the opposite.

"It is raining."

That sentence is either true or false depending on the weather. Now flip it:

"It is NOT raining."

If "It is raining" is TRUE, then "It is NOT raining" is FALSE. And the other way around.

NOT is a one-part operation. It only takes one piece of sentence and flips it. The whole sentence changes value when you stick NOT in front of it. NOT is logic that you use everyday!

The Truth Test

Two rows. That's the whole truth table. Try it below — pick a truth value for the sentence and watch NOT flip it.

Only two rows. NOT is the simplest of the four words.

A Real Example

"I am tired."
"I am NOT tired."

These two sentences can't both be true at the same time, and they can't both be false. One of them is always true, the other always false. They're opposites in a clean, total way.

Tricky Bits

1. NOT NOT cancels.

"It is NOT NOT raining."

That's just "It IS raining." Two NOTs cancel each other out. Like flipping a coin twice — you end up where you started.

2. NOT only flips ONE part — where you put it matters.

"It is raining AND the sun is shining."

Put a NOT in front of the whole thing: "It is NOT (raining AND the sun is shining)" — that flips the entire AND statement.

But this is different: "It is NOT raining AND the sun is shining." — that only flips the raining part, leaving "(NOT raining) AND (sun shining)."

Where you put the NOT changes which piece gets flipped. We'll handle this carefully in Module 2.

3. English uses NOT in lots of disguises.

• "I never do that." — NOT ever.
• "Nobody came." — NOT anybody.
• "Nothing happened." — NOT anything.

All hidden NOTs.

Recap

• NOT flips a sentence's truth value.
• TRUE becomes FALSE. FALSE becomes TRUE.
• NOT NOT cancels out — you're back where you started.
• Where you put NOT in a complex sentence matters. Parens decide which part gets flipped.