Logical Propositions
What are they?
They are sentences that can have only two values:
✅ True (T)
❌ False (F)
There is no “more or less true”
Examples of propositions:
“2 + 2 = 4” → True
“Lisbon is in Brazil” → False
“10 is greater than 5” → True
What is NOT a proposition
Sentences that cannot be judged as true or false:
❓ Questions → “What time is it?”
📢 Commands → “Close the door”
😮 Exclamations → “What a beautiful day!”
These do NOT belong to logic
Types of propositions
Simple proposition
A single idea:
“It is raining”
“John studies”
Compound proposition
Combination of two or more ideas:
“It is raining and it is cold”
“John studies or works”
Every proposition must:
Be a declarative sentence
Have complete meaning
Be classified as T or F
⚠️ Common trap
Sentence:
“x + 2 = 5”
This is not a proposition because it depends on the value of x.
Quick summary
Proposition = sentence with a logical value (T or F)
Cannot be a question, command, or emotion
Can be simple or compound
It is the foundation of all Logic
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