Welodd e ddim ohoni - ddim + the preposition o are shortened to mo and placed before a definite object in Welsh when using negative verb forms, e.g.
welais i ddim + ffilm neithiwr = welais i ddim ffilm neithiwr (indefinite)
welais i ddim + y ffilm neithiwr = welais i mo'r ffilm neithiwr (definite)
When the definite object is a pronoun (he, she, them …), i.e. a word used to replace a noun that has already been mentioned, the preposition o conjugates as follows in a negative context:
| mohono i | Welaist ti mohono i. | You didn't see me. |
| mohonot ti | Welais i mohonot ti. | I didn't see you. |
| mohono fe/fo | Welais i mohono fe/fo. | I didn't see him. |
| mohono hi | Welodd e mohoni hi. | He didn't see her. |
| mohonon ni | Welsoch chi mohonon ni. | You didn't see us. |
| mohonoch chi | Welodd hi mohonoch chi. | She didn't see you. |
| mohonyn nhw | Welais i mohonyn nhw. | I didn't see them. |