There's a couple ways to know your way around these better.
(1) -ton always derives adjectives and hence nouns or verbs will have epä-: here so in 'injustice', 'despair', 'disorder', 'to fail'. — Or also you can derive further from the adjective: e.g. äärettömyys 'infinity' (ääretön means 'infinite').
(2) -ton always signifies a lack of its base. Helps here e.g. with 'unhealthy' which is something that is unhealthy to you and not lack of health.
(3) -ton normally attaches to a noun (toivo, ääri, raha, aika, kuri, lohtu…) and so adjectives with no base noun and no antonym will take epä-: here so in 'impolite', 'surreal/unreal', 'unstable', 'unsure'. (A few other words of this sort are epäaito 'ingenuine', epäpyhä 'unholy'; also epätyhjä 'non-empty' as the mathematical term.) Also indeed 'unhealthy' since not just terveellinen 'healthy (to someone)' but also its base form terve 'healthy (agent)' are adjectives.
Now if wanted, you could still start appending -ton also to property names in -us, e.g. varma → varmuus 'certainty, security' → varmuudeton 'without certainty / securities'; or terve → terveys 'health' → terveydetön 'healthless', if someone were just having every disease at once or something.
Note also that you have three affixes here, not just two. Huolimaton, tyytymätön, voittamaton are not derivatives in -ton, they're derivatives from the verbs huolia, tyytyä, voittaa with the compound suffix -maton (there are no nouns **huolima **tyytymä **voittama — though these are their 3rd infinitive stems of course). This is productive for all verbs: you could also have toivomaton 'unhoped', järjestämätön 'unordered', kiistämätön 'undisputed', onnistumaton 'unsuccessed', etc.; note in particular uskomaton 'unbelieved' which is also used as 'unbelievable'.
Occasionally two options are still possible though. A synonym for 'hopeless' is indeed epätoivoinen (= epätoivo+inen; there is no **toivoinen, 'hopeful' is toivokas). Similarly e.g. epäkelpo / kelvoton 'unfit, improper' (and yes that's an exceptional -ton derivative from a base adjective, sorry about that).
theartofmadeline
2087
gummygunk
pixelskylines
