F2L Deduction Guide
Start with what you know
You can recognise any piece in isolation from 2 stickers. This means you can recognise every piece in the following H configuration without looking at the back or turning the cube. If you're struggling to recognise corners from just two stickers, practice using the corner recognition game, or read the corner recognition guide
Using deduction
While we cannot recognise the 5 1-sticker pieces in the back in isolation, we can often deduce them from the wider context.
Corners
We can already recognise 3 of the 4 F2L corner pieces from the H. It just so happens that they all have visible white faces, but we can recognise them without them. The final corner must be hiding in one of the two 1-sticker corner slots.
The last F2L corner to find is the orange-green corner, so it must be in the back-left because the back-right shows a green sticker.
Edges
We can only recognise two of the F2L edges from the H.
We're left to find the red-green and orange-green edges. We know they are both hiding in the back.
We can quite easily deduce that the orange-green edge must be in the top-back, and the green-red edge must be in the back-right. With that, we have found all of the F2L pieces without checking the back or turning the cube.
Faster deduction
You don't need to find all the recognisable pieces before you can start deducing the 1-sticker pieces.
Counting colours
At the stage of F2L, we've already solved the four cross pieces. This means there are only three edge stickers for each side colour remaining.
If we can see three green edges, we know none of the hidden edge stickers are green. Likewise, if we can see 2 green edge stickers, we know one of the 1-sticker edges is green, and so on.
Take our example from above. Let's say we're looking for green-red.
The edge isn't in the H, and two of the 1-sticker edges look viable. However, by noticing that there are exactly two visible green stickers, we know that there must be one more hidden in the back. It's not green-yellow because we can see that piece, so it must be hiding on the red 1-sticker edge.
If we had been looking for the green-orange edge, we could have spotted that there are exactly two visible orange stickers and deduced that it must be the top-back slot without needing to know anything else about the cube.