In the few piano pieces I've learned, I've sometimes seen notation ambiguous to me whether or not to play the notes immediately preceding slurs as legato.
For instance, the treble clef in bars 3 and 4 from Burgmüller's La Pastorale:
Bar 3 is clearly understood. The slur for the treble clef encompasses the entire bar. It follows the end of the slur of bars 1 and 2. So, I interpret this as "lift the right hand at the end of bar 2, play the notes in bar 3 legato, and then lift the right hand at the end of bar 3, ready for bar 4".
However, bar 4 is less clear. There is a slur, but only covering the last three notes of the treble clef, and excluding the dotted crotchet D. To me, there seems to be two different ways this could be read: which is the most appropriate?
1. Play the D legato into the slur, so all notes in bar 4's treble clef are played legato, i.e. play the notes as in bar 3.
My argument: I've learned a general rule-of-thumb in piano to play notes legato, unless they are marked deliberately not. (I realise this is not an absolute and may depend on the composer or period when a piece was written.)
2. Play the D and then lift off, before playing the three notes in the slur legato.
My argument: why would the D not be included in the slur if it is intended to be played legato into the other notes? Wouldn't the notes in bar 4 just all be notated under a slur as in bar 3 to indicate they are all legato?