3.263 The meanings of primitive signs can be explained through elucidations. Elucidations are propositions which contain primitive signs. They can thus only be understood if the meanings of these signs are already known.
What the…?! This sounds circular and pointless. Don’t know the meaning of a primitive sign? An “elucidation” will help. But you will only understand it if you already know the meaning of the relevant primitive sign! So either knowledge of meaning is not the same thing as understanding when it comes to signs, which seems unlikely (but who knows?). Or explanation of meaning is quite impossible (in the terms presented by the Tractatus up to now). See p. 44 and pp. 49-50 of Joan Weiner’s essay in Future Pasts.
Anscombe (p. 26) suggests that this passage, along with 3.261, provides the best evidence for thinking that the elementary propositions of the Tractatus are simple observation statements, such as “This is a red patch.” Names and only names are primitive signs. Logical signs, as he indicates elsewhere, are not primitive signs. But (see p. 27) what elucidates a name need not be an elementary proposition. And from 6.3751 it follows directly that “This is a red patch” cannot be an elementary proposition. Anscombe concludes that elementary propositions are not simple observation statements, and that this explains why Wittgenstein did not refer to observation in connection with them. What they are he cannot say, but they must exist. See, for instance, 5.5562, 3.23, 2.021, 2.0211, and 4.221.
See also 5.526.