"tomato sauce" vs. "tomato paste" [duplicate]

Tomato sauce and paste are not the same thing.

Tomato paste is essentially a concentrated tomato with some water removed that is then preserved. It is generally only used as an ingredient.

Tomato sauce is immensely variable and usually has a variety of other ingredients added resulting in something to actually eat.

Tomato paste is basically mashed up tomato pulp (no seeds or skins) baked to form a paste with some citric acid. When sold in a store it usually comes in 6-8 oz cans. Look at the ingredients:

Tomato Paste, Citric Acid.

Tomato sauce is basically hydrated tomato paste with a small amount of added seasonings. It usually comes in 15-16 oz cans. Look at the ingredients

Tomato Puree (Water, Tomato Paste), Water, Less Than 2% Of: Salt, Onion Powder, Garlic Powder, Citric Acid, Natural Flavors, Dehydrated Bell Pepper.

The seasonings are fairly mild. I've seen recipes that will take either and tell you to just add water if using the paste.