Mynd a Gwneud – Dyma 'berfau afreolaidd' sy'n hollol wahanol yn yr amser gorffennol, e.e:
I went > Es i
I did/made > Gwnes i

Fel rheol, dyw'r sain 'gw' mewn ffurfiau 'gwneud' ddim yn cael ei hynganu ar lafar. Felly, byddwn ni'n gallu meddwl am ffurfio amser gorffennol 'gwneud' drwy ychwanegu 'n' at ffurfiau amser gorffennol 'dod', fel hyn:

Es i (I went)
Nes i (I did)
Est ti (You went)
Nest ti (you did)
... ac yn y blaen.
Mynd a Gwneud – These are irregular verbs and change completely in the past tense e.g:
I went > Es i
I did/made > Gwnes i.

The ‘gw’ in gwneud is not usually pronounced in speech. To form the past tense of ‘gwneud’, simply add the past tense forms of ‘mynd’ to (gw)n-, e.g (gw)nes i, e.g.

Es i (I went)
Nes i (I did)
Est ti (you went)
Nest ti (you did)
... and so on.
Yr Amser Gorffennol Rheolaidd

Er mwyn ffurfio amser gorffennol y rhan fwya o ferfau eraill, bydd terfyniad yn cael ei ychwanegu at fôn y ferf, fel hyn:
-ais i ('I did' something)
-aist ti ('you did' something - ti)

Ar lafar, bydd yn sain Gymraeg 'ai' yn swnio fel 'e' yn Saesneg, felly ar lafar, byddwn ni'n dweud:
-es i ('I did' something)
-est ti ('you did' something - ti)
The Regular Past Tense

To form the past tense with nearly all the other verbs, an ending is added to a root:
-ais i for I did something
-aist ti for you did something (ti)

In speech the ‘ai’ sounds like an ‘e’:
-es i ('I did' something)
-est ti ('you did' something - ti)
Yr Amser Gorffennol Rheolaidd - Bôn y Ferf

Rywbryd bydd y terfyniadau hyn yn cael eu hychwanegu'n syth at y berfenw, e.e:
edrych (to look) > edrychais i > edrychais i > I looked
darllen (to read) > darllenaist ti > darllenaist ti > You read
chwarae (to play) > chwaraeais i > chwaraeais i > I played

Gyda berfau eraill, bydd rhaid i ni ddefnyddio 'bôn' neilltuol. Byddwn ni'n gwneud hyn drwy ddileu'r llafariad olaf, neu'r sillaf olaf, cyn ychwanegu'r terfyniadau, e.e.

Codi ('to get up') > cod- (bôn) > codais i > codais i ('I got up')
Cysgu ('to sleep') > cysg- (bôn) > cysgais i > cysgais i ('I slept')
The Regular Past Tense – Roots

Sometimes these endings are added straight on to the verb, e.g:
edrych (to look) > edrychais i > I looked
darllen (to read) > darllenaist ti > You read
chwarae (to play) > chwaraeais i > I played

With other verbs, a ‘root’ is formed, usually by dropping the last vowel or syllable, before the endings are added, e.g:
Codi (to get up) cod- (root) > codais i > I got up
Cysgu (to sleep) cysg- (root) > cysgais i > I slept