Fact

A fact is a statement that is real or true, or a thing that can be shown to be real or true. That is its core meaning, though the word has a long history, and has been used in many ways.Shorter OED, p667. 

A fact is something that has really happened or is actually the case. The usual test for a statement of fact is whether it can be shown to be true. Standard reference works are often used to check facts. Scientific facts are verified by careful observation or measurement (by experiments or other means).

 Facts as statements 
A fact is a statement (a claim) about something that is true. A fact can answer questions like, "what color is it?" or "who made that?"

An opinion is different from a fact. But you can say facts about a person's opinion. For example, someone can ask a question like "What is Alice's opinion about the book?" You can answer this question with a fact, for example "Alice said she likes the book." Then it is a fact that Alice says she likes the book. But maybe Alice does not like the book. So it is not a fact that Alice likes the book, but it is a fact that Alice says she likes the book.

One way to learn a fact is if a person can help you see it. For example, if you ask, "do you have my book?" To answer this question, a person can let you see your book. Then you can know it is a fact that this person has your book.

 Examples of fact statements 
These examples show that there are facts of different kinds.
 Your heart pumps blood through your body.
 Africa is a continent.
 There are more men than women in the world.
 The leaves of growing plants are usually green.
 Some people keep dogs as pets.
 1 litre of water weighs 1 kilogram on Earth.
 There are 50 states in the United States.

 False statements 
 Water always comes from the sky.
 Dogs are made of bone.

 Scientific theories 

A scientific theory is knowledge of important facts about a natural thing. The facts in a scientific theory have evidence that shows that the fact is not false. 

A person who understands the scientific method can test to see if the facts of a scientific theory are correct. When statements have been tested and shown to be not false, they may be "true". The facts of each scientific theory have usually been questioned and tested by many people. Because of this, we know that the knowledge of a scientific theory is fact and not opinion. Examples of scientific theories include the theory of relativity and the theory of evolution. More simply, it is a fact that the Earth goes around the Sun (and not vice versa). This took so long to establish because a leading religious body had the reverse opinion (see articles on Galileo and Copernicus for the story). Now we can say that there is a difference between statements of fact, and opinions or claimed truths of religion. The difference is in the way disputes about the truth are decided.

 References 

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