spanishskulduggery: Anatomy of Spanish: A direct object [objeto directo] is the part of the sentence
spanishskulduggery: Anatomy of Spanish: A direct object [objeto directo] is the part of the sentence that receives the action. In other languages that have case systems, direct objects are known as “accusative”. Direct objects are used for the sake of brevity, when the object is known there’s no need to include the noun itself. In Spanish, a masculine direct object can be substituted for lo in singular, and los in plural. A feminine direct object can be substitued for la in singular, and las in plural. The direct objects stand in for definite articles (el libro / la flor = “the book” / “the flower”) or for indefinite articles (un libro / una flor = “a book” / “a flower”). Pay special attention to where the direct object goes when it's lo / los or la / las - before the verb. In English, direct objects are often translated as “it” or “them”. But sometimes direct objects can be people; in English it would be something like lo conozco “I know him” or la conozco “I know her” instead of the longer sentence. *Note: It’s totally okay, and is probably preferable, to just say compro un libro / lo compro and leave out the yo. This is just done for the sake of being specific; the compro only exists in present tense yo so there’s no confusion as to what the subject of the sentence is. If it were 3rd person compra you might have to specify if it’s “he”, “she”, or “You (formal)”, or compran “they (masculine / masculine + feminine), “they (feminine only)”, or “You all”… but the other conjugations (compro, compras, compramos, compráis) only apply to one potential subject. -- source link