Full Idea
Only a sentence with the time-specification filled out, a sentence complete in every respect, expresses a thought.
Gist of Idea
A sentence is only a thought if it is complete, and has a time-specification
Source
Gottlob Frege (The Thought: a Logical Enquiry [1918], p.343(76))
Book Reference
Frege,Gottlob: 'The Frege Reader', ed/tr. Beaney,Michael [Blackwell 1997], p.343
A Reaction
I take the 'every respect' to include the avoidance of ambiguity, and some sort of perspicacious reference for the terms. I wish philosophers would focus on the thoughts in their subject, and not nit-pick about the sentences. Does he mean 'utterances'?