How are observation and inference different

When you see a tall, young, skinny man walking along the beach, you

observe that a tall, young, skinny man walked along the beach, and from

your observation, you know that a tall, young, skinny man walked along

the beach.

When you see a beach with nobody there, but there is a line of 5-toed

footprints in the sand along the beach, you infer that a human being

walked along the beach. If you are a skilled anthropologist, with some

talent and experience in a few other fields whose names escape me at

the moment, you might be able to make some careful measurements of

the length, width, depth, and shape of the footprints, and then you might

be able to infer that the person who walked along the beach was a tall,

young, skinny man. You would build all of your information from inference,

without any observations at all except for the line of footprints and your

measurements of them.