Using the Word 'Difficulty' Correctly

I came by this sentence today while doing an edit:

• B. F. Skinner's operant conditioning shows the difficulty to change someone's habits by giving negative punishment.

At first glance, there seems to be nothing wrong with this sentence, especially to us non-native speakers of English. However, as you can guess with the title, the error revolves around the word 'difficulty' and that murky concept surrounding gerunds and infinitives. 

You see, the expression [to have difficulty] is one among a special group of expressions that are followed by a verb-ing or a gerund. A gerund is a noun formed from an -ing verb which usually refers to an activity (ex. swimming, hiking), process (ex. aging, weathering) , or state (believing, loving). We then have the structure:

• Subject/Somebody [has difficulty + verb-ing] something.  

Here are examples:  

• The committee had some difficulty deciding the theme of this year's exhibit. 
• Are you having difficulty memorizing your lines?
• I hope you won't have any difficulty settling in to your new school. 

Note though, that we can also use the preposition "in" when using this expression, as in:

• have difficulty (in) doing something

There is no difference in meaning whether we choose to include "in" or to leave it out. Here is a very helpful screenshot from the Longman Dictionary of Contemporary English Online. At the very bottom of the photo, which we have highlighted with the green box, it specifically says that we should not use this expression with a to-infinitive and say [has difficulty to do something]. 

Applying this rule about using gerunds with 'have difficulty', we can then go back to our sentence earlier: ​

• B. F. Skinner's operant conditioning shows the difficulty to change someone's habits by giving negative punishment. 

and improve it by saying:

• B. F. Skinner's operant conditioning shows the difficulty in changing someone's habits by giving negative punishment.

If you are interested in this special group of expressions used with gerunds, find more examples in the following blog post:

• ​Special expressions + verb-ing

Feel free to practice writing your own sentences with the expression [have difficulty + verb-ing in the comments below!