Those of you who, like me, are mature enough to remember Schoolhouse Rock will recall that a pronoun is a word that takes the place of a noun, because “saying all those nouns over and over can really wear you down”. I tried once to go an entire day without using pronouns, and found that I couldn’t make it ten minutes unless I counted the time I wasn’t speaking.
Antecedent is probably based on some Latin thing, and I’m not going to bother to look up the actual origins, but it means the word the pronoun is replacing. For the record, I had several books published before I even heard the word “antecedent” or learned its meaning.
The antecedent doesn’t even have to be in the same sentence, for example, “Sally went to the store. She bought bread, milk, and eggs.” “She” is the pronoun; it replaces the noun “Sally” in the second sentence. In this pair of sentences, there is no doubt that “she” means “Sally”. It would be redundant to say “Sally went to the store. Sally bought bread, milk, and eggs.”
The problems begin to arise when the antecedents are too far from their pronouns, or there are other ambiguities. For example, “Sally went to the store with Martha. She bought bread, milk, and eggs.” We can see that Sally is at the store. Martha is also at the store. However, Sally and Martha are both female names, so it is unclear which one of them bought the groceries. Sally is the subject of the first sentence, so the pronoun in the second sentence should refer back to her, but Martha’s name is closer to the pronoun, so there’s really no way to tell which one of them did the purchasing.
If the sentence becomes, “Sally went to the store with Thomas. She bought bread, milk, and eggs,” it is clear that Sally is doing the buying, because Thomas is male, therefore the pronoun belongs with the female name. However, if Sally goes to the store with Drew, we have a problem because there’s no way to tell if Drew is male or female.
When writing, be careful that your pronouns are near enough to your antecedents for your meaning to be clear. If the meaning is not clear, by all means, restate the antecedent rather than use the pronoun. It’s far better to be redundant and understood than have someone throw your writing down in exasperation because they don’t know who you are talking about.