The features of a use of language may be considered by considering its field, tenor and mode. The field is also referred to as the experiential metafunction. It is how language is used to make meaning about the world - in other words, the actual content of what is being communicated.
One might naively think that this was all that language was - the communication of information - but it is more subtle than that. Every language event takes place between one or more participants, and in addition to communicating information, language events are used as part of the process of enacting interpersonal relations. This is tenor, also referred to as the interpersonal metafunction. Additionally, language events can take place in many different forms (conversation, email, a sermon ...), and these are themselves largely detached from both field and tenor. This textual metafunction is the mode.
So, what does this mean in practice? Let's take this blog post.
- Field - I am attempting to explain, in fairly simple terms, information about the theoretical use of language.
- Tenor - I'm addressing unknown readers (who are you? Say hello!), but I'm writing in a fairly informal style - I'm assuming that the average reader will just have happened across this, and wants to read something that's engaging, friendly and not too heavy. Frankly, that's how I like communicating anyway, and since this is my space, really written for my own amusement, I guess I do what I want.
- Mode - a blog post. Written language can be more planned and deliberate than spoken language, for a start - there's a definite structure, and I've assumed in writing it that people will start at the beginning and read through hopefully to the end!
You can imagine changing each of those individually would change the way in which language was used. For example - suppose (field) I was writing about something else, maybe a film review? Or suppose (tenor) I knew that the people reading this were children aged 12? Or suppose (mode) I was delivering this as a talk? Each of the metafunctions, then, has a bearing on how language is used, and this linguistic structure is something that has only really been described in the last 30 years or so.