This is an important empirical properties.

This is an importantly empirical properties.

Which one is correct? Do they mean different things?


3 Answers 3


You need important.

But more importantly: neither sentence is correct due to the plural properties.

These are important empirical properties


This is an important empirical property


As mplungjan noted, you need to use the plural form (or the singular form) consistently, but in either case, important is the word you want to use.

Important and importantly are two different words: the first is an adjective (similar to quick, happy, stunning), the second is an adverb (similar to quickly, happily, stunningly). As a general rule (there are exceptions), adverbs can be created from adjectives by adding the -ly suffix: so usually (although again, there are exceptions), if you see a word ending in -ly, it is an adverb.

Adjectives describe nouns (He is quick), while adverbs describe verbs (He runs quickly). Since property is a noun, you need to use an adjective in your sentence.

So, the two correct sentences would be:

These are important empirical properties.

This is an important empirical property.

That said, you could also use importantly in two similar-looking sentences:

Importantly, these are empirical properties.

Importantly, this is an empirical property.

Here, the word in question is modifying the verb (is), and not the noun. However, the meaning of these sentences is different: in this case, you're not saying the properties are important, but that the fact that they're are empirical properties is an important fact.


[I prepared this but the question was migrated before I updated the screen...]

Neither is correct, and they do mean different things.

Correcting is easy: This, is and an are singular so properties needs to be singular as well (property); or, if there really are properties, then you should have These are or perhaps These are some.

This is an important empirical property.
This is an importantly empirical property.

Important is an adjective and describes a noun, property. The property is important as well as being empirical.

Importantly is an adverb. Adverbs do not describe nouns in the same way; but they can modify adjectives. Using importantly describes empirical; it does not say anything directly about the property. We might infer that the property is important, but what is definitely important is that it is empirical. It's not a particularly good example to try to explain the difference, because importantly empirical doesn't mean very much.

A better example might be

This is an important packaged product.
This is an importantly packaged product.

In the first sentence, the product is important and packaged. In the second, importantly describes packaged: the package makes the product look important.

The difference might be made clearer with commas and hyphens, but the usages of adjectives and adverbs fix the meaning well enough without them.

This is an important, packaged, product.
This is an importantly-packaged product.

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