Natural gender
English follows what is called "natural gender."
This means that a word is masculine if it refers to a male (e.g., "he") or feminine if it refers to a female (e.g., "she"). If a word refers to something that is neither male or female, it's gender is neuter (e.g., "it," "book").
Some nouns change their form depending on gender. For example, we say that the King's son is a "prince," but if the queen had a baby girl we call her a "princess." What are some other examples of words that change their form depending on gender?
But the vast majority of nouns are considered neuter. We don't think of a book as a "he" or a "she"; we think of a book as an "it." What are some nouns, however, that we think of as a "she"?