It must be remembered also that he who can talk with himself has no need of another’s conversation.

[Etinim, qui secum loqui poterit, sermonem alterius non requiret.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

Tusculan Disputations [Tusculanae Disputationes], Book 5, ch. 40 (5.40) / sec. 117 (45 BC) [tr. Peabody (1886)]
    (Source)

(Source (Latin)). Alternate translations:

For he that can speak with himself; will not much need the Discourse of another.
[tr. Wase (1643)]

Whoever can converse with himself doth not need the conversation of another.
[tr. Main (1824)]

For the man who can speak with himself, does not require the discourse of another.
[tr. Otis (1839)]

Whoever can converse with himself doth not need the conversation of another.
[tr. Yonge (1853)]

One who can converse with himself will not miss the conversation of someone else.
[tr. Douglas (1990)]

He who can talk to himself, will have no need of another’s conversation.
[tr. @sentantiq (2012)]

A man who is able to hold conversation with himself will not need another with whom to converse.
[tr. Davie (2017)]