The structural principle

The structural principle of classifying phraseological units is based on their ability to perform the same syntactical functions as words. In the traditional structural approach, the following principal groups of phraseological units are distinguishable:

Verbal (the head word is a verb)

e.g. to run for one's (dear) life,

to get (win) the upper hand

Nominative (the head word is a noun)

e.g. dog's life,

cat-and-dog life,

calf love,

white lie,

birds of a feather.

Adjectival (the head word is an adjective) e.g. high and mighty, brand new, safe and sound.

In this group the so-called comparative word-groups are particularly expressive:

(as) cool as a cucumber,

(as) nervous as a cat,

(as) weak as a kitten,

(as) good as gold,

(as) pretty as a picture,

as large as life,

(as) slippery as an eel,

(as) drunk as an owl (sl.),

(as) mad as a hatter/a hare in March.

Adverbial

e.g. by hook or by crook,

in cold blood,

in the dead of night,

between the devil and the deep sea.