A Question On Relative Pronouns & Conjunctions

Solution 1:

The two 'that's are simply demonstrative pronouns. Each conjunct of your sentence has the same basic structure as:

• He who hesitates is lost.

In this sentence, the 'he' is a pronoun, and the 'who' is a relative pronoun. In your second conjunct:

• That which starts bitter ends sweet.

'that' is a pronoun, and 'which' is a relative pronoun.

In the first conjunct:

• That that starts sweet ends bitter.

the first 'that' is a pronoun. The second 'that' is traditionally called a relative pronoun, but many linguists (including myself) would say that it is simply the subordinating conjunction (or complementizer) 'that'.