索性: might as well, simply (go all the way)
【高41】语气副词 / adverbs
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
索性 (suǒxìng) expresses the decision to go all the way rather than carry on half-heartedly: the situation is already bad, or the half measure is pointless, so you pick the clean solution. English: "might as well just…", "may as well…". It follows a clause that gives the circumstance and often takes 就: 衣服已经被雨淋湿了，我索性就合上了伞，直接在雨中散步了.
The choice is the speaker's own (or the subject's) and it is a sharp one: stop, cut, do it all at once. 他说了半天也没人听，索性不说了. You hear irritation or bravado in it, rarely enthusiasm. Without a circumstance to justify it, 索性 sounds wrong: you cannot say 天气很好，我索性去公园.
Compare its close cousin 干脆 (HSK 5): both mark a radical decision, but 索性 leans on a situation already under way or compromised, and is only an adverb, whereas 干脆 can also describe a straightforward person (他说话很干脆). Compare 不妨 too ("no harm in", a polite, light suggestion): 不妨 proposes without committing, 索性 decides.
Examples
说了半天他也不听，我索性不说了。
Shuō le bàntiān tā yě bù tīng, wǒ suǒxìng bù shuō le.I talked for ages and he wouldn't listen, so I simply stopped talking.
反正已经迟到了，我们索性慢慢走，不赶了。
Fǎnzhèng yǐjīng chídào le, wǒmen suǒxìng mànmàn zǒu, bù gǎn le.We're late already anyway, so we might as well walk slowly and stop rushing.
衣服早就湿透了，我索性把伞收了，在雨里慢慢走回家。
Yīfu zǎo jiù shī tòu le, wǒ suǒxìng bǎ sǎn shōu le, zài yǔ li mànmàn zǒu huí jiā.My clothes were soaked through already, so I simply put the umbrella away and walked home slowly in the rain.
现在已经很晚了，我索性在外面吃完饭再回家。
Xiànzài yǐjīng hěn wǎn le, wǒ suǒxìng zài wàimian chī wán fàn zài huí jiā.It's very late already, so I might as well finish my dinner out before going home.
这台电脑修了三次还是坏，我索性就换了台新的。
Zhè tái diànnǎo xiū le sān cì háishi huài, wǒ suǒxìng jiù huàn le tái xīn de.This computer broke down again after three repairs, so I just replaced it with a new one.
你既然这么想去，索性现在就订票吧。
Nǐ jìrán zhème xiǎng qù, suǒxìng xiànzài jiù dìng piào ba.Since you want to go so badly, you may as well book the tickets right now.
Common mistakes
✗ 天气很好，我索性去公园。 → ✓ 下雨了，我索性不出门了。 (索性 needs a circumstance that justifies going all the way: a situation already bad or a pointless half measure).
✗ 你索性去。 → ✓ 你索性去吧。 (to urge someone to settle it, the sentence normally ends in 吧).
✗ 他索性很高兴。 → ✓ 他索性不干了。 (索性 introduces a chosen action, not a state).