ers (since), erbyn (by the time), cyn (before), ar ôl (after), wrth (while/as), rhag ofn (in case), nes/tan (until), hen bryd (high time)

Bydd yn bosibl defnyddio'r adroddiad 'i' gyda phob un o'r geiriau neu'r ymadroddion uchod, i gyfleu sawl ystyr, e.e:

Cyn i fi fynd
Before I go/have gone/went.

Erbyn iddo fe gyrraedd
By the time he arrives/has arrived/arrived.

(Mae’n) hen bryd i ti fynd
(It’s) high time for you to go/you went

Wrth iddi hi gyrraedd
As she arrives/arrived

Tan/nes iddyn nhw gyrraedd
Until they arrive/have arrived/arrived

* Ar lafar, bydd pobl weithiau'n defnyddio 'bod' yn lle 'i' yn yr amser presennol, e.e.

Cyn bo’ fi’n mynd – Before I go.

Fel arfer, bydd pobl yn defnyddio 'Gwell' ('better') fel hyn, e.e.

Gwell i chi fynd – you had better go, Gwell i ni fynd – We’d better go, etc.

Rhaid (must)

Pan fydd pobl yn dweud 'rhaid i' drwy'r amser, sylwch ar y ffaith y bydd 'i' yn cyfleu amser gwahanol yma. Ar lafar, yn yr amser presennol, byddwn ni'n hepgor 'mae'n' fel arfer.

(Mae’n) rhaid i ni fynd. We have to/must go.
(There is) a necessity for us to go

Roedd rhaid i ni fynd. We had to go.
There was a necessity for us to go

Bydd rhaid i ni fynd. We will have to go.
There will be a necessity for us to go

ers (since), erbyn (by the time), cyn (before), ar ôl (after), wrth (while/as), rhag ofn (in case), nes/tan (until), hen bryd (high time)

The preposition ‘i’ is used with all the above, and can convey several tenses, e.g:
Cyn i fi fynd
Before I go/have gone/went.

Erbyn iddo fe gyrraedd
By the time he arrives/has arrived/arrived.

(Mae’n) hen bryd i ti fynd
(It’s) high time for you to go/you went

Wrth iddi hi gyrraedd
As she arrives/arrived

Tan/nes iddyn nhw gyrraedd
Until they arrive/have arrived/arrived

*In speech ‘bod’ is sometimes used for the present tense instead of ‘i’, e.g:
Cyn bo’ fi’n mynd – Before I go.

Gwell (better) is only usually used as below, e.g:
Gwell i chi fynd - you had better go, Gwell i ni fynd - We’d better go, etc.

Rhaid (must)

Although ‘i’ is used, the tense is changed as below. In speech, the present tense – ‘mae’n is usually omitted.

(Mae’n) rhaid i ni fynd. We have to/must go.
(There is) a necessity for us to go

Roedd rhaid i ni fynd. We had to go.
There was a necessity for us to go

Bydd rhaid i ni fynd. We will have to go.
There will be a necessity for us to go