How to say "speculate" in Japanese

• 山をかけるやまをかける
  expression, ichidan verbCovers 'speculate' in the gambling sense: making an educated guess that is really a bet, as on getting the right questions. A less common idiom, seldom the default choice for the verb.
• 山を張るやまをはる
  expression, godan verbMuch the same as 山をかける: it covers the gamble-on-a-guess sense of 'speculate', such as betting on getting the right questions. Equally idiomatic and less common, so the two are effectively interchangeable.

Both are less common idioms covering the same sense of 'speculate' — gambling on an educated guess, as on getting the right questions — so either works there, while other senses call for different words.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 山をかけるやまをかけるto speculate
• 山を張るやまをはるto speculate