Tim Evans wrote:NASB capitalises the Him to clarify who is known by who.
Wrong, that's not why it is capitalized. But let's not discuss English translations here.
Still, let me mention one thing about English. A better title for this thread would be "who knows whom?" In sentences like "he knows me", "I know him", or the (awkward) sentences "Him I know", it's clear who knows whom from the form of the words. Greek is like that too. You won't be able to figure this out without working systematically through a Greek grammar.
Tim Evans wrote:Is there something about greek grammar or one of the words in this sentence that allows us to know who loves who?
That's really too broad a question to discuss. You need to dig into the Greek far enough to ask specific questions about words or grammatical questions, not just "is there anything there". What are you doing to learn the Greek language?
εἰ δέ τις ἀγαπᾷ ⸋τὸν θεόν⸌, οὗτος ἔγνωσται ⸋ὑπ᾿ αὐτοῦ⸌. (1 Cor 8:3)
I'll give you a hint about the kinds of things you will learn. Take a look at τις and τὸν θεόν. One of these forms is functioning like 'who', the other is functioning like 'whom'. In the first chapter or so of a Greek grammar, you can learn about nominative and accusative cases. Here's one you could use:
http://greek-language.com/grammar/04.html
ἐξίσταντο δὲ πάντες καὶ διηποροῦντο, ἄλλος πρὸς ἄλλον λέγοντες, τί θέλει τοῦτο εἶναι;
http://jonathanrobie.biblicalhumanities.org/