<img src="https://i.sstatic.net/CQoPu.png" width="72" alt="2-methylaniline"> <img src="https://i.sstatic.net/j6qW6.png" width="83" alt="2-methylbenzoic acid"> When comparing *o,m,p*-toluidine basicities, the *ortho* effect is believed to explain why *o*-toluidine is weaker. But when comparing *o,m,p*-toluic acid basicities, the *ortho* effect is stated as a reason why *o*-toluic acid is stronger acid. I was told that the *ortho* effect is a phenomenon in which an *ortho-* group causes steric hindrance, forcing the $\ce{-COOH}$, $\ce{-NH2}$ or some other bulky group to move out of the plane, inhibiting resonance. Then, if the *ortho* effect inhibits resonance, why is *o*-toluic acid the strongest and *o*-toluidine the weakest? Where am I going wrong in my understanding of the *ortho* effect?