[mesmark]

Corpora are databases of language and you can use them to look up frequency of collocations to get a sense of 'native' gramaticality.

There are some set up databases and websites you can hop onto that will do this. For example if you want to see what the most common word to follow 'such a ooo' is or 'too OOO to OOO' is, you can using their database and search functions. You can also test what is more common and get a sense of frequesncy between two similar phrases. 'since a year ago' and 'since last year.' They're good for curriculum design.

I don't use them because I can check frequency using google's search function which is quite similar. The up and down side of that is that it is a lot of web language. While it contains a lot of natural speech/writing it also contains a lot of poor grammar and errors.

Was that the question?