1♠ - 2♦  -3♠  - 4♣ is a common problem sequence. Every time I sit down to play with a good player in the County and this sequence comes up I know I am in for a murky time. The question is - is 4♣ a cue or a second suit? I would like to suggest the following as a standard version, based on responder only wanting to show a second suit with at least 5-5. There are three basic sequences:

1. Minor jump rebid: The only way to agree a minor jump rebid is to raise it. For example, 1♦ - 1♠ - 3♦ - 4♣  is natural. If you wanted to agree diamonds, raise them!

2. Two level response over one of a major:

1♠ - 2♦ - 3♠ - 4♣ is a cue unless responder's next bid is 5♣, 6♣ or 5NT, all showing big minor two suiters. Opener responds initially as to a cue. Thus 1♠ - 2♦ - 3♠ - 4♣ - 4♦ - 5♦: The 4♦ bid was a cue, as is 5♦, since responder did not bid 5♣.

1♠ - 2♦ - 3♠ - 4♦ is natural.

1♠ - 2♦ - 3♠ - 4♥ is a cue (unlikely to want it as natural since with 5-5 would respond 2♥ ).

1♠ - 2♦ - 3♠ - 5♣ is a splinter raise.

1♠ - 2♦ - 3♠ - 5NT is 5-6 with the red suits!!

Note that 1♥ - 2♣ - 3♥ - 3♠ ♠ ♠ is basically natural, looking for 3NT.

3. 1♥ ♥ -1♠ - 3♥ : The only sequence left, and a special one. Four of a minor is a cue here. With a big two suiter, rebid 3♠, and then if partner raises leap to six of a minor.