I am struggling with the sometimes conflicting uses of 先


Rikaisama's definition of 先 includes meanings like _previous; prior; former;
some time ago_. However it also includes meanings such as _front; ahead; the
future; destination_. I am struggling to make sense of when to apply each
meaning since it seems to me that they are pretty much the two sides of the
same coin in one word. There's also 先に which can mean before; earlier than /
ahead; beyond, among others.

I've noticed that if the meaning has to do with the past, the subsequent verb
is in the past tense. This is a good starting point, but it doesn't always
help me. Am I forced to learn each usage of 先 individually or is there some
"rule" to the word that would help me identify it's meanings in different
contexts?

Thank you in advance.




# The rule between "prior" or "posterior"

You can judge the usage of `[先]{さき}` in a sentence if there is `これから` before
`先` or not.

If there is `これから`, `先` expresses the posterior time.

If there is NOT `これから`, `先` expresses the prior time.

# Exaplanation of the usage of `先`

There is a big hint that `[先]{さき}` expresses the RELATIVE past / future.

I show you how `先` is used:

> Figure 1: "I do X before I do Y."
>
> ![I do X before I do Y](https://i.stack.imgur.com/PPMhJ.png)

* * *

> Figure 2: "I'm doing X before I do Y."
>
> ![I'm doing X before I do Y](https://i.stack.imgur.com/rBtP0.png)

* * *

> Figure 3: "I did X before I do / am doing / did Y."
>
> ![I did X before I do / am doing / did Y.
> ](https://i.stack.imgur.com/nfjdM.png)

* * *

> Figure 4: "I do X in the future."
>
> ![I do X in the future](https://i.stack.imgur.com/RAlAz.png)

Please take a look at Figure 1 through 3. If you say `Yより先にXをする (I do X before
I do Y)` or simply `先にXをする (I do X before something/sometime)`, you're
mentioning that you do X before you do Y or something. ("prior" usage)

Next, please take a look at Figure 4. If you say `*これから* 先にXをする (I do X in the
future)`, you're mentioning that you do X in the future. ("posterior" usage)

The difference between the "prior" usage and "posterior" usage is that you say
with `これから` or without.

`先に` without `これから` doesn't mean future in ordinary usage.

As a result, you can judge the usage if there is `これから` or not.

# Answer to @dainichi 's comment

My answer is a point of view and doesn't cover other cases like he says.

I'd like to say that, `先` with following `に` acts like an adverb while `先`
with `が` acts like a **noun**.

## `先` with `が`

This is an idiomatic usage but not so special in terms of syntax. For example
`先が思いやられる` is passive expression and can be converted into active one.

Important: There's no usage that `先` means prior thing if `先` acts like noun.

> [先]{さき}が[思]{おも}いやられる = （[私]{わたし}は）先を思いやる (Translation: I worry about
> future.)
>
> 先が[見]{み}える = （私は）先を見る (Translation: Watching the tip of long thing. Watching
> distant place.)
>
> 先が[長]{なが}くない = 先は長くない (Translation: One has not long to live.)

This proofs that `先` acts like a noun with following `が`.

## `先` with `この`

`この` is similar to `これから` and are swap-able. It's hard to explain but `これから`
sounds more explicit and longer span of time; speaker is talking about things
to happen _from now on to far future_.

> この先、[雨]{あめ}が[降]{ふ}るだろう。 (It will rain soon.)
>
> これから先、[彼]{かれ}は[立派]{りっぱ}な[大人]{おとな}になるに[違]{ちが}いない。 (I guess he'll become a
> respectable person.)

