Before the 1800's people didn't have right or left shoes.  They had shoes of just one shape that they used for both feet.  When people first saw right and left shoes, they laughed.  They called them "crooked shoes."  "What a silly idea," they said.  You can tell that shoes before 1800:

What does Inference mean?

Every four years, February has an extra day.  When this happens, it is called Leap Year.  But even with the extra day, February is still the shortest month of the year.  Some months, like June and November, have 30 days.  Other months like March and August, have 31 days. 
It is likely that:

It was raining outside. Sue got out of bed and got dressed for school. Then, she ate breakfast and grabbed her backpack.  Before Sue left the house, she probably ___________________.

Amy opened the door to the bathroom. “What is that dripping sound? Why is the carpet wet and squishy all around the bathtub? The rest of the carpet is dry. Oh no!”
What is the problem?

Macey's mom noticed that she was squinting as she read her book, which was only a few inches away from her face. She scheduled a doctor's appointment for the next week, and when the doctor said Macey needed glasses, she tried on every single pair in the office. After spending an hour looking at glasses, mom suggested that perhaps she should sleep on it and come back and decide in the morning. Macey agreed, but she kept talking about the pros and cons of each pair all night long. 
What can you infer about Macey?

As the teacher lectured the class about how important it was to pay attention, Brian found himself staring out the window again. Suddenly, a little boy came up to the window and peeked in. The boy blew a bubble with his gum and it exploded all over his face and the window. Brian began laughing so hard he fell out of his seat. The rest of the class silently stared at him as the teacher walked to his desk.
What can you infer about how the teacher will react?

Every day after work Paul took his muddy boots off on the steps of the front porch.  Alice would have a fit if the boots made it so far as the welcome mat.  He then took off his dusty overalls and threw them into a plastic garbage bag; Alice left a new garbage bag tied to the porch railing for him every morning.  On his way in the house, he dropped the garbage bag off at the washing machine and went straight up the stairs to the shower as he was instructed.  He would eat dinner with her after he was "presentable," as Alice had often said.  
What type of relationship do Paul and Alice have?

In real life, people who can back up an opinion about a text with Textual Evidence are taken more seriously than people who can only give a reason of “just because".

To make an inference, we use evidence from the text, and our prior knowledge. 

When writers do not state the way a character feels, the writer will include details that readers must use to make inferences or form opinions about how a character feels. When you make inferences, you use:

Albert stormed into his apartment and threw down his lunchbox. He had just lost his job. Albert had worked for the same company for over ten years. But today he was informed that he was no longer needed. Albert didn't know what to do.  
Based on what you have read, you can INFER  that:

What can you "infer" by reading the passage below?

"I hate the idea of having all those people out there watching me...I just don't like it when I'm around so many people. I wish I just could hide somewhere," whispered Violet.

The toothbrush as we know it today was not invented until 1938. However, early forms of the toothbrush have been in existence since 3000 BC. Ancient civilizations used a "chew stick," which was a thin twig with a frayed end. These 'chew sticks' were rubbed against the teeth. The bristle toothbrush, similar to the type used today, was not invented until 1498 in China. The bristles were actually the stiff, coarse hairs taken from the back of a hog's neck and attached to handles made of bone or bamboo. Boar bristles were used until 1938, when nylon bristles were introduced by Dupont de Nemours. The first nylon toothbrush was called Doctor West's Miracle Toothbrush. Later, Americans were influenced by the disciplined hygiene habits of soldiers from World War II. They became increasingly concerned with the practice of good oral hygiene and quickly adopted the nylon toothbrush. What can you infer about the nylon toothbrush?

Eight people are carrying a large inflatable down the bank of a river. The water in the river is moving very fast. Each person buckles up their life preserver and puts on a helmet. They climb into the raft and paddle to catch the rapid current.  
What do you think the eight people are doing?