Is it simple or is it hard? For your hard thing to do, you must make a thing for a computer to do that finds out if some words are explained in a simple way. Something is explained in a simple way if it only uses the ten hundred most used words. If not, it is explained in a hard way. This can be a full computer thing or part of a computer thing. (full program or function)

There is a thing for a computer to read that has all of the ten hundred words in it with a space between each word. The name of the thing for the computer to read is called 'most used.txt'. You can take this thing from this computer place.

The person who uses the computer thing will enter some words. (This can be from STDIN, function arguments or command line arguments) The computer must say something like a true if the words are simple and something like a not true if it is hard. (truthy-falsy) The person who makes the shortest thing for the computer to do is the best. The things that every person knows are bad are bad. (standard loopholes apply)



More stuff to know about how the computer thing works:


It doesn't matter if the words are BIG or little.
The pictures that make what the word meaning easier to know (punctuation) don't matter. So if the person who uses the computer thing says "dont" it isn't a different word than the word "don't". Numbers and other pictures also don't matter. So if the person says "HE$$ll9o" the computer should read it like "hello"
The little lines between words (dashes) work the same way as spaces. So the word "up-goer-five" is the same as the words "up goer five".




More stuff to know about making words like this:

https://xkcd.com/1133/

http://splasho.com/upgoer5/#
R, 106 bytes

Is not sure if is understand challenge because is has hard time reading.



function(s){u=toupper;all(strsplit(gsub("[^A-Z -']","",u(s)),"[ -]")[[1]]%in%u(scan("most used.txt","")))}


This creates an unnamed part of a computer thing that accepts a string and returns something like a true or like a not true.

Ungolfed + explanation:

partOfAComputerThing &lt;- function(s) {
    # Remove everything but letters, spaces, dashes, and single quotes
    s &lt;- gsub("[^A-Z -']", "", toupper(s))

    # Split s into a vector on spaces/dashes
    v &lt;- strsplit(s, "[ -]")[[1]]

    # Read the file of words (assumed to reside in the current directory)
    m &lt;- scan("most used.txt", "")

    # Determine if all words in the input are in the file
    all(v %in% toupper(m))
}


Thanks to Dennis for inspiration thing.