The neuter article (lo)

In Spanish, nouns are either masculine or feminine. However, there is a special "neuter" article: lo.

You never use lo with a noun. Instead, pair it with a masculine singular adjective to turn that adjective into an abstract noun. This is equivalent to saying "the [adjective] thing" or "that which is [adjective]" in English.

The only thing is that we have no money.
Lo único es que no tenemos dinero.
The main thing is that one must always study.
Lo principal es que hay que estudiar siempre.
The strange thing is that there is someone here.
Lo extraño es que hay alguien aquí.

Specifying the context

To talk about the good, bad, or interesting part about a specific thing, use lo + adjective + de (of/about). Remember that de + el combines to form del.

The fun thing about the trip is the beach.
Lo divertido del viaje es la playa.
The good thing about the hotel is the breakfast.
Lo bueno del hotel es el desayuno.

Pros and cons

Another common way to discuss the positives and negatives of a situation is by using the nouns la ventaja (the advantage) and el inconveniente (the disadvantage).

The advantage is the price.
La ventaja es el precio.
The disadvantage is that it is complicated and nobody understands it.
El inconveniente es que es complicado y nadie lo entiende.

You can easily mix these nouns and the neuter article lo to weigh the pros and cons of any situation!

The fun thing is the trip, but the bad thing is the traffic.
Lo divertido es el viaje, pero lo malo es el tráfico.

Contributors