Here, you have five keys to know how and when use neutral article ‘lo’, that create many doubts to students of Spanish.
1. No name is accompanied by ‘lo’ because all names in Spanish only have male and female gender.
2. You can find neutral article ‘lo’ before an adjective, an adverb, a prepositional syntagma or a relative clauses with ‘que‘.
“Lo antes posible”.
“Lo de hoy”.
“Lo que te dije”.
3. ‘Lo’ can accompany adjectives of male or female gender.
“Lo pequeño”, “lo pequeña”
“Lo malo”, “lo mala”
“Lo bueno”, “lo buena”.
4. Lo + adjective refers to concept that adjective expresses. Also, it can express ‘quantity’.
‘Lo bueno es beber dos litros de agua’. (It is healthy drinking two litres of water daily).
‘Llevo lo justo para comprar el pan’. (I have the amount of money necessary to buy bread).
5. In other situations, you can listen or read the structure ‘lo de + noun’, used when something or someone is named in an indirect manner, and that speakers supposed to know.
‘Siento mucho lo de Andrés’. (I am very sorry what happened Andres).
‘Me enteré de lo de tu padre’ (I found out what happened to your father).
Madrid, Sandra Municio /Practica Español