A oscuras, a tientas, etcétera

[Tyrn]

Hi,

I've got a growing collection of such use cases:

a oscuras
a tientas
a ciegas
a cuestas
a medias

I've got two questions:

1. What's the name of this grammar thing?

2. Are they all set phrases of an established list, or can one make them freely?

[aleCcowaN]

They are instances of locuciones adverbiales (adverbial phrases). You could not make them freely.

There are many starting with the preposition a. There are many more constructed in a different way:

de cuando en cuando = every now and then
de cabo a rabo = from head to toe
en mi vida = never

Many of them may be replaced by a proper adverb:

a horcajadas (loc. adv.) = acabalgadamente (adv.)= astride (prep.)
sin duda = indudablemente = undoubtedly

[Tyrn]

So the family is wider than I expected

Another, more specific question:

a oscuras

What is a and what is -as?

[aleCcowaN]

a oscuras/obscuras = in the dark

I don't know the reason but many of these expressions using adjectives become nouns are plural and feminine:

a ciegas = blindly (literally)
a oscuras

but other expression use nouns in plural (or singular) of any gender

a tientas = blindly (it literally means "by using the sense of touch")
a gatas = crawling (on your hands and knees)
a pedazos = in pieces
a gusto = comfortably

[Tyrn]

Thanks! The meaning is obvious, usually. Except for a gatas . Do they mean cats?

[aleCcowaN]

Yes, it comes from gato. It's used to suggest "in a quadruped way".

[Tyrn]

There is also a very expressive verb gatear